White lithium grease?? I'd try greasing the metal "ears" behind the mirror first. Does the motor move easily with the mirror detached? If so, the ears need the grease.
The motors on the 08's seem to be a problem area. I had an issue with mine and after many attempts to locate the problem I just replaced both motors. In hind sight I would have done that first as the time spent was far more than the cost of the replacement parts.
That's not right...I have memory mirrors and that was more expensive and they were $115.00 each from my dealer parts department . The other style was about $90.00. That was a few weeks ago and online pricing will be less.