My left rear window is stuck in the halfway down postion on my '85 300TD wagon. Actually, it will go down, but will not go up. I've replaced window motors before on these but before I take the door apart, how do I diagnose the motor or should I just assume it is the motor? I ask because when these have failed in the past, they've always stopped working in either direction.

Oh, also I have tested and ruled out both switches.

I should just keep a stockpile of window and antenna motors -harv