older Chamberlain/Craftsman reversing feature has stopped working

[LOBfan13]

I have a Craftsman (Chamberlain) 1/2 hp vintage garage door opener. The Sears model # is 41A-3493-1. It has an integrated sensor in the unit...no jamb mounted external sensors.
I installed it 3 yrs ago to replace a similar Genie unit. I adjusted both the length of travel controls, as well as, the up and down force controls at installation to meet specs. It would reverse upon hitting an obstruction w/ no problem.
Fast forward to now. I recently took ownership of the property, after leasing it for two years. Upon checking the door's function, the reversing feature longer works. The opening and closing feature is still fine. I have tweaked the up/down force controls in multiple combinations and cannot attain the level of sensitivity I once had. Either the door stops, w/ no reverse, upon hitting an obstruction, or it auto reverses w/ the slightest hitch in the door movement as it lowers.
I am a re-modeler and have some, but limited, experience w/ installing and tweaking similarly aged units. I have tried all I know and have read about this unit and have reached a dead end. I am hoping someone reading this can offer a more experienced analysis of my problem.
Am I overlooking something?
Thanks

[TJR]

All get's older. More use and wear. Lube all the hinges, roller/roller shafts and moving points. Open/close the door by hand to check if door sticking or binding. Look closely at the door on the out side for damage and cracks. With cracks the door can flex so much that it will not reverse.
Adjust the door arm to be close to vertical, adjust the down force as low as possible, but still so you can close the door, then adjust the close limit 1/4 till the door reverse on a 2x4 laid flat on the floor. Move the 2x4 and close the door to test it will stay close.

[LOBfan13]

All get's older. More use and wear. Lube all the hinges, roller/roller shafts and moving points. Open/close the door by hand to check if door sticking or binding. Look closely at the door on the out side for damage and cracks. With cracks the door can flex so much that it will not reverse.
Adjust the door arm to be close to vertical, adjust the down force as low as possible, but still so you can close the door, then adjust the close limit 1/4 till the door reverse on a 2x4 laid flat on the floor. Move the 2x4 and close the door to test it will stay close.

Thanks for taking the time to respond.
I can relate to falling apart as I age.
I greased the tracks, sprayed lubricant (wd40) onto the shafts of the wheels, made sure the vertical tracks are tight and parallel, and made sure the door is balanced. I've adjusted the down force to its absolute minimum, just before it catches almost immediately when going down, from the raised position.
When you say "adjust the close limit", do you mean the "down travel limit"? I fiddled w/ that a bit, but will give it another go.
The door is a 16' wide metal door, w/ no insulation...very light...so it tends to react to the slightest resistance in the track and will waddle a bit. It has always worked though, including the reversing feature, until now.
I'll take another look at the top panel. It did give a bit when I first installed the opener. That was because there was no strut in the package (home depot purchase). I quickly stopped the opener and waited to re-enforce it before engaging the motor again. After putting the strut on, the door opened fine, did not buckle and cycled as it should. That was 3 yrs ago.

[TJR]

When you say "adjust the close limit", do you mean the "down travel limit"? Yes.
What position is the open and close force dial at?
When you open the door is it like it drop in as it go up and overhead and the again when you close the door it pop up?
Any door and opener manufacturer recommend reinforcing the top section(with a strut) when installing an electric operator, but only most doors over 12' come with a strut for the top section.

[LOBfan13]

In describing where the up and down force settings are, I'll use a clock face analogy.
The left setting knob (I think it was the up setting...I'm not at the house it's located at so I can't verify), is set around the 7 o'clock position. The right knob/down is about the 3 o'clock position. I mentioned before that the down force is set about as minimum as I can set it w/out nuisance stops. It does not reverse like it used to...it just stops in place.
I forgot to mention my door is in sections, four separate panels.
I did not get an opportunity to fiddle w/ it today. I hope to tomorrow.
Thanks for the followup.

[TJR]

When we get a new opener both force setting dials is just about 4. Look at the door and see how much it flex/buckle when it hit the 2x4. Many times when I can't make it reverse it's because of damage to the door.

[LOBfan13]

I had too many distractions yesterday to attempt any tweaking.
THanks for your settings. I"ll try those as my default and work from there.
I am having difficulty understanding your comment about damage to the door. Looking at my door, you see nothing but flat panels. I know it has a hint of a crease at the attachment point of the opener, but to the casual observer, it isn't seen...very minimal. And the door has worked as it should for 3 years.
Can you explain how door damage keeps it from reversing? I am familiar w/ your 2x4 test. Since the door does not reverse, it just jambs itself into the 2x4. When you refer to buckling...how can it buckle? It is in tracks on either end, so how is it going to buckle? The entire set of panels bow out a little bit from the force of the motor, but the door does not buckle, per se.
I also grab the door bottom when half way down to simulate an obstruction. The dang thing does not respond. I was convinced it was a setting, at first. Now, you are making me think it is the door, but I don't understand how. Is the concept based on the panels being so bent that the force isn't concentrated enough in the up and down axis to trigger the reversing feature? By that, I mean the force of the motor is dissipated at the damaged areas by the loss of integrity of a flat panel...instead of a directed force, it becomes less focused because it is disrupted by the bent panel. Maybe I can grab a pic of mine to show how intact my panels are.
On another topic, the ignition on my truck starter is giving me problems and that is my focus, at the moment. I need the truck to move some furniture today or tomorrow.
I'll post when I've addressed the opener again. Thanks

[TJR]

Look at the picture HERE and HERE
If you have any damage like that it can compromise the strength of the door.
Disconnect the opener from the door so you can open/close by hand. Go outside and then open/close the door and as you do so look for black lines as in the first picture in between the sections. You might not have the crack on front of the door, but in between on the bottom and top of the sections.
Mostly when a opener don't reverse is because the door is damaged and then you can replace the opener with almost any out there and still have the same problem.
I have see force dials go bad and it go from nothing to max in 1/2 minute on the dial. You should be able to stop the door as you did half way down, but as you do also keep an eye on the top section to see how much it get push down ward by the opener.

[LOBfan13]

Informative. I"ll look between the edges. I try to take a pic. I had no luck tweaking yesterday. Frustrating.

[LOBfan13]

I have given up tweaking. Weird that I can't get the auto reverse to engage anymore.
Here are a few pics of the door, just to bring this discussion to a close. In no way is the door damaged enough to transfer the jar of a stoppage peripherally, which, evidently disables this feature.
Thanks for the help.

[TJR]

Nice door, don't look bad at all. So with what you told so far and what I can see in your pictures will rule out the door as the problem.
Some might run tight on/in the opener. Did you or any ever tighten the chain on the opener? Get the ladder out and look up on top of the opener around the front of the drive sprocket, do you see a little pile of black stuff? Take the cover of the opener and take a good look at things to see if gear or bushings has any wear. A couple drops of oil (3in1, engine oil, oil) on the motor shaft at the bushing behind the black cap, on the drive shaft at the bushing under the white gear and drip some oil on the pulley at the wall mount you will see where it can seep down. Some times that can free up an old lady. It can be some in the dials. Before pulling to much hair swing by Home Depot and see what they have of Chamberlain openers.

[LOBfan13]

I adjusted the chain properly at installation, three years ago. It's not slack or too tight. I'll look the areas you mentioned, for curiosity's sake. I am selling the house this unit is in and had to give up a few bucks in negotiating for the thing not reversing. Pissed me off. I don't have to touch it again, except for my own satisfaction in knowing why it is failing and if I could remedy the problem.
Thanks for those tips and your help along the way. You were most helpful. Having a pro acknowledge it is simply a tweakable fix is comforting. The inspector convinced the buyer they needed a new door and operator, which is total BS.