Chain keeps getting stuck on stop bolt despite multiple adjustments

I have a LiftMaster 1/2 HP opener (purple learn button) and it is a couple years old. For whatever reason it keeps getting stuck on the stop bolt. It used to only happen once every couple months but now it is happening once every one or two weeks. It is very annoying to have to get a ladder out, loosen the chain, ... I have played around with the up and down distance dials on the side, the force dial on the back, ... nothing seems to work long term. After I "fix" it, I will run in 4 or 5 times and it works perfect (stops 4-6 inches away from the stop bolt). But then within a week or two it gets stuck again.

Any thoughts?

 

Could be a worn sprocket. Google "Chamberlain, Liftmaster, Sears Gear and Sprocket Replacement". There is a site with step by step instructions. You might look at those steps and then see if yours has any of the same wear patterns.