What would cause a headlight motor to go bad? I mean what inside the motor itself. Not the gears and bushings.

My original motor had a bad arm/rod that was sometimes freespinning when the motor turned on. Sometimes not. Anyway, replaced the motor with a junkyard special. Rebuilt it, bushings and all that. Now, occasionally it decides it doesn't want to go up. The motor doesn't make a peep. Sometimes playing the drums on the headlight door help, but only if you flip the switch again after doing that. Meaning it won't just go up on its own by rapping on the door/motor. If I manually turn the motor to the up position, it will always go back down with the switch and will work for a time normally up and down. The light does turn on, but the motor doesn't always do anything.

I've also replaced the headlight switch last week. Being old and the letters worn off, it couldn't hurt to have a new one. That didn't help either. Replaced the headlight door module as well.

I am curious what could go wrong in the motor itself to cause this. I've had it with home rebuilds and junkyard motors, so I'm going to try with a new or rebuilt motor. What would be a better choice? Cardone rebuilt or a new AC Delco that includes the linkage? Since it's the right motor, it's the only one AC Delco still sells.