Ensure your motor is working. Run wires directly to the motor contacts (you'll have to remove the door panel to access them). If your motor is bad you can replace it with a used one for $35.00 from mercedesdismantlers.com . Just make sure you get the right motor with the same number of teeth. I got a couple of motors without any problems.
Probably not related to the problem under discussion, but another failure mode for power windows.
I have disassembled '82 330SD for repaint. I also had a window problem that I must repair to pass inspection. The plastic piece that pushes the window up, and pulls it down was broken. ( Piece is on the end of the regulator arm and slides in the channel along the bottom of the window.) Further investigation found that the rubber-like pad that is glued to the door skin had peeled away from the door at its top edge. When the window came down, it hit the ( very stiff) edge and stopped the window from moving. The motor kept running broke the plastic piece.
If you have your doors apart, you may want to shine some light in there and see if the pad is secure.
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