My GMC sierra side mirror is loose on from the amr. The mirros is fine it is the little swivel that is looses and the mirror constantly moves. I am unable to remove the mirror to get to the problem.

I just spent about 2 hours trying to resolve the same problem, and discovered that there doesn't appear to be any way to repair the mirror without purchasing a whole new one. There a 3 screws you can access by slanting the mirror to the extemes in both the up or down positions. Once they are removed I discovered a 4th screw (once I broke the plastic pieces surrounding the mirror appart) that there is a 4th screw that is impossible to reach without removing the actual mirror part. In any case I discovered that the reason that the mirror was floppy is because there was a funny looking nut that is supposed to lock in the spring mechanism that was completely stipped and non functional. Better luck than me!