Its probably a switch problem. The early ones can be taken apart and cleaned if one is handy with such things.
If the motor is working but the seat isnt moving you have a cable problem most likely. The cable housing stretches and eventually one end comes out of the gearing at either end. I have fixed many of these cables by taking a quarter inch out of the center and then placing a piece of fuel hose (7.5mm ID) and two clamps over the two ends. The only reason to do this is that the seat is out and the dealer doesn't have the cable as they are relatively cheap.
Bosch Master, ASE Master, L1
33 years MB technician