How to replace your glass
Get the replacement mirror glass. I think I have seen them on eBay if you cant find them local. To replace, push your mirror in towards the hinge with your hands as far as it goes. Using a flashlight look inside the mirror assembly. You will see that there is a round part to the back of the mirror with multiple tabs going around the perimeter. Take a long, thin, flathead screwdriver and gently work the tabs loose, one at a time. After you loosen a few of them the tabs get easier to work loose, allowing you to pop off the mirror. Then, just snap down the new mirror on the exposed mount.
Oh, and if you have the heated glass, just unplug the old mirror and plug in the new one, then snap it onto the mount.
Here are a couple of pics to show you the mounts