Sounds like you have some gears slipping underneath there somewhere.
Sorry I cant help out all that much. I just bought a 91 Z28 and am soon to
replace the power window motors. Iv had the door panel off for a while now
trying to figure out how to get the project done.
Just thought it would give you a visual of what is underneath the panel:
My 92 RS had exactly the same problem last month. It's the gear on your motor.
The one which intersects with the sector teeth on the regulator.
Good news is: Your motor itself is probably fine.
Bad: The gear is part of the motor assembly.
Replace the motor assembly. Solved the problem for me.
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