The motor is behind the door panel at the bottom front,a common fault with ALL motors is that the brushes wear and lose contact with the commutator,if you strip it down and clean the commy it will probably work,you don't need to remove the motor,take the back off pull the brushes back and unscrew the commutator from the body,clean the copper segments of carbon and re-fit,it is a bit of a fiddle but a new motor will cost you £250 fitted probably.I fixed one a year ago and it's still ok.
Rich
May 2008