I've removed the glass from manual mirrors. Basically the trim ring around the glass is bonded in a few places to the shell of the mirror housing. There is no trick to removing the glass, and unfortunately no way to do it cleanly.

I pryed the trim ring off by using a wide flat-bladed screwdriver. By working slowly around the perimeter and loosening a little at a time the ring can be removed without breaking, but there are no guarantees. Also, it is virtually impossible to prevent buggering up the plastic with the screwdriver; removing the burrs will be required. You will need to glue the pieces back together when the glass has been replaced.

The only reason I even bothered with the project is that I had a couple of new mirrors with broken glass and a couple of old mirrors that had lost their ability to stay in position despite being tightened. It seemed to make more sense to have 2 good mirrors instead of throwing 4 in the trash. For most people it's probably better to just spend the $25 on a new one.

-Alex