There are a couple of reasons that the rear windows don't work properly...

On the 123's, 124's and the 201's, the wiring that goes from the pillar to the door wiring can break...this can be an easy fix. While holding the window switch, open and close the door slowly...if the wiring is the problem, you find out because the window will begin working.

The other problem is a bit more trouble. Because some of these motors were not well insulated from moisture, the shaft will rust to the bushing in the inside bottom of the motor. The bushing will then spin in the motor housing. The motor will run, but the housing will get really hot where the bushing is on the inside of the motor housing...you'll know it if when you touch the bottom of the motor, it's really hot.

I've tried to repair the rusty shaft problem on a number of occasions, but the best solution is a good used motor.

Hope this helps....

The Tenor Man

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Currently Driving.....
1987 Mercedes Benz 300D Turbo - Daily Driver.
2004 Buick Rendezvous...Smaller than it looks!
2005 Mitsubishi Galant - Not bad for a tin box...Lousey Seats
Past Vehicles.....
1994 Dodge B-250 Van- GAS HOG..Succumbed to rust!
1989 Mercedes Benz 260E - Totaled but no one injured.
1977 Mercedes Benz 240D - Loved it, but SLOWWW! - Succumbed to RUST!
1976 Mercedes Benz 240D - Same as above! -
1975 Mercedes Benz 240D - Same as above!