There are plenty of descriptions in this Forum about how to remove the door panel and check this. I had a similar problem, but my window motor was shot. Prices for these vary A LOT. I think I paid under $80 locally for a new Bosch motor. I had to solder the connection wire, but it wasn't as hard as I expected.

Good luck!

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)