The wires in the conduit might be broken or the connections might be bad.
The grounds are under the driver and passenger seats, respectively.

Slamming the door leads me to think conduit plug.

 

Thank you. I was leaning the same way.

But now I have an excuse to delay tackling this. A while back my SS right rear window failed and the fix was a new regulator. Wouldn't you know just a couple weeks later the left rear quit. So a couple days ago I got around to tearing it apart and it is indeed another broken regulator. The part is on order, same brand as the last one, mirror image m, five bucks more for no good reason. I actually look forward to doing this one. The other one was kinda fun.

The top should look more like the bottom. I guess after 13 years, the plastic fatigued or got brittle and broke. Exact same failure. See my comment #21.

I don't know how these work. Do they just stall at the end of travel? Or is there something in the circuitry that shuts them down when when current draw reaches a certain value, or something?

The motors seemed fine so I removed them before I threw away the broken regulators, in case someone needs one.

 

There seems to be a limit switch in the motor. You can strangle a kid with his head out the window; There ought to be a law.
I just had my cataracts removed and can't see the small stuff.