If you have any wiring knowledge whatsoever, you can verify if the motor is good or not. On my '85 300D, I took the power going into the switch and jumpered it directly to the motor. Be advised that you need to just momentarily touch the motor wires to hear if the motor starts to drive. The way the motor works is +12v is provided to the motor to make window go down. To make the motor drive the window up, the polarity of the +12v is reversed. If your window is currently up, you wouldn't want to continuously drive the motor to put the window up. This may cause the motor to burn out or strip some gears, etc. So by just momentarily providing the +12 you will at least hear the motor start, therefore letting you know the motor is OK.
84 500SEL EURO 87K
85 300DT 267K (not my miles tho)