Generally I agree with Jules but I have had some success seperating the mirrors..This is a cut & paste that I saved after typing it out repeatedly a few years ago...


step 1 disassembly, just slap the mirror housing on a piece of wood, mirror side first, a mirror in motion tends to remain in motion usually a couple solid whacks is all it takes.
the hard part is getting the mirror back in the housing, the first trick is seperating the mirror glass from the metal backing, two methods have shown moderate success, heat breaks down the adhesive sometimes, also soaking the mirror & backing plate in laquer thinner may break down the adhesive, I've never had much luck with either method, I generally just break the glass, most glass shops can cut a new one or Resto Rick sells them, he can even provide one with a date code if your the type that cares.
As long as you have the glass out nows a good time to deal with another common problem with these mirrors, the pivot tends to get loose due to the peened anchor attachments for the pivot fail, you can drill through the center of the anchors & install a 6-32x3/4 bolt & locking nut in each location problem solved
After the housing has been painted & before gluing the new mirror in the backing reinstall the backing in the mirror housing, apply a few drops of red loc-tite to make sure the mirror stays, then just tap the backing plate into the mirror housing, then glue the mirror lens in its backing with either silicone or urethane & you should be good to go!

Posted soon after by gygeneral the original poster of this thread
I tried your suggestions, it worked great!!! The only additional step I took was to soak the splined pin in WD40 for a day before I tapped the mirror against a piece of wood. First the glass came off without breaking, then a few more slaps and out came the base.

thanks again!!!