I've got stock original mirrors on my CB500. The glass on the left mirror fell out on me when I was riding around in the yard just after I first got the bike up and running. It's a big yard, 1 1/2 acre, took me awhile to find the glass but find it I did and it was intact. The rubber in between the mirror glass and the metal is what apparently holds them in, this rubber had cracked and shrunk enough that it would not hold the glass snug anymore, so I put some silicone high temp gasket sealer on it to "glue" the glass to the rubber. This mirror vibrates enough that at freeway speeds everything is a blur, but the right hand mirror stays perfectly clear.
MJ