I don't know if it's ok, but I am just linking what I put into another site, as that site allows posting of pictures directly, and I'm too lazy to start uploading to a hosting site and do all the work again.
https://www.k-bikes.com/threads/replacing-a-cracked-mirror-on-a-k1200gt-or-any-bm-with-mirror-stalks.48732/And here is the text as well
Firstly, kudos to Boxertrix.com for the information regarding putting it in the oven.
Note: this is what I did, you do this at your own risk to your bike, health, and marriage. Use oven gloves etc.
Anyway, while I was backing out the K, I caught the mirror edge on a shelf and cracked the glass.
Thus started the investigation. You can buy the whole assembly, possibly second hand, but why, when it's just the glass that's cracked. You cannot buy the glass separately, but luckily I had two mirrors from replacing my wife's Audi glass with heated mirrors.
so, here is the procedure i used.
1. Remove the stalk from the bike, and remove the lower mechanism/nuts/springs etc.
2. Heat the oven to around 170 degrees C. Some have used 200, some 150, try a bit of trial and error. If the plastic surround isn't flexible enough, up the temperature.
3. Put the stalk in for about 10 to 15 mins.
4. The mirror surround should have expanded and be much softer when you take it out.
5. The mirror should fall out, or be easy to lever out with a thin screwdriver.
6. If you use an old car mirror, remove the plastic backing from the mirror if necessary
7. Use the old mirror as a template for the new mirror. Note that the new mirror is convex, so keep the same horizontal plane if possible. I stuck a piece of paper on the old glued back when I took off the plastic.
8. Bring the new mirror to a glazier to have them cut it out.
9. It is suggested to paint nail varnish or something similar around the cut back edges to stop moisture getting in.
10. Heat up the stalk again and pop the new mirror in place, job done. Be very careful and don't force it. I cracked the first attempt, but luckily I had two Audi mirrors, so just cut the other one. If it is not popping in, turn up the heat and try again.
Once the stalk has cooled down it will shrink a bit and the mirror will sit better.
11 Put mirror stalk back on the bike.
A couple of notes.
Some people suggested using normal mirrored glass. I'd recommend using car or bike mirrors. These are concave and give a much wider view.
Also, If you find it easier to get a second hand replacement cheap, but you can only get the wrong side, buy and use the process above to pop out the mirror and put it into your broken one. In most, if not all, cases, the mirrors are symmetrical on the horizontal axis, so the left hand and right hand ones are swappable.
All in all, not too difficult to do, just take your time and don't force anything as it is easy to crack the mirror. You shouldn't cause any damage to the stalk up to 200 degrees C.
(Usual caveats apply - you do this at your own risk).
