1985 300D. Bought it two weeks ago at auction for $1500. Everything works (don't know about antenna as radio/speakers are missing - it was a police impound). Anyway, put driver's rear window down yesterday and it wouldn't go back up. I tried both console and door switches. No motor noise. I tried gently but 'deliberately' 'tapping' the door's metal case thinking it might be a struck motor but no dice. So I left it down overnight and today. Tonight in the garage, just for grins, I turned on the ignition and tried the console switch again. Nothing. Then I lowered and raised all 3 other windows from the console switches. The I tried the rear door switch again and BINGO, it went up, where it will stay until I can figure out why. It did appear to go up somewhat slow but that could be my imagination, or maybe a track in need of lube or a tired motor?

Hypotheses?