Hi Paul,
It is very easy to replace the glass, I have done it twice, the first time the mirror was replace with a 2mm glass and it worked great, but it cracked after a few months, so now I have put in 3mm glass and glued the little plastic thingy you see in the pictures. The only problem with using the 3mm is that you can't switch to night view using the little button at the bottom of the mirror.
Go to a glass shop with your old glass and they will make it for you.
If need more instruction, I'm glad to help.
Rich