I just replaced the right mirror assembly on my 1996 K1100RS. I have to say I have been disappointed at several stages during the process. The mirror was completely missing when I bought the bike. The previous owner said it was damaged when he dropped it in his garage. I purchased an OEM "Mirror Assembly" online for just North of $200. When I received it, I was dismayed to find that a "Mirror Assembly" does not include the mirror glass. I called the dealer, and after some checking, I was told that indeed the mirror glass does not come with the "Assembly". Personally, I would have called it a housing instead of a mirror assembly. Anyway, I ordered the glass and decided to paint the housing while I waited. It came out beautifully, if I do say so myself. I received the mirror glass, waited a couple of days for the paint to dry then started re-assembly today. No instructions came with the housing or the mirror glass. The glass did come with a spring clip, but no pictures or directions explaining how to use it. I couldn't see how to access the back of the glass to install the pin. So I hit the net. The only video I could find was for a K100 but the guy briefly mentioned the pin for the 1100RS units. I found this thread. I thought "Awesome!" I had found the information I needed. Someone said something about separating the two halves of the housing. Tried that, didn't work. Someone else said, "Yeah, it's glued. You really have to pry hard." Did that. Got it apart. Screwed up my beautiful paint job.
Then I discovered (this is the juicy part) the new housings come with a spring clip pre-installed. All I needed to do was press the mirror glass in until the clip snapped in. No disassembly required.
Sometime this winter, when I'm not riding, I'll repaint the housing. But for now, all I can hope is that my story saves someone else the grief I experienced because BMW doesn't include simple installation instruction or drawings (no translation required) with their replacement parts. By the way, I own a repair manual for this bike. It does not cover mirror replacement.
Ride safe,
Nolo