I've had a similar problem with my driver's side in the past. Does it move occasionally, or not at all? Sometimes it is a simple matter of opening it up, cleaning it up and greasing the motor. When I first purchased mine the mirror did not work at all. The seller took it to their mechanic and had it opened up, and the aforementioned was all that was required. Works now for the most part.
---------- Post added at 03:46 PM ---------- Previous post was at 03:42 PM ----------
Also, I believe it is a single motor for the whole assembly. Someone is welcome to prove me wrong though, I have not looked in a long time.