The gears/limit switches in a Chamberlain/Craftsman/LiftMaster opener are easily replaced and a common thing to go out.

Good call on the force adjustment - but it should be adjusted so that it reverses on a 2x4 laid flat but enough to open/close the door. Also, lube the rail, a tiny bit grease on the bottom of the T-rail(LiftMaster) or dry spray lube on the square tail(Chamberlain and Craftsman) works fine.