Hi, yes blistering of the mirror base is a very common problem. Mine, and my friends Z3's both suffered the same problem. We have now refurbished both cars and really are as good as new. If I was you I would definately not paint them black for starters. I would prefer to keep them standard and I think more asthetically pleasing. It's a really easy job, door cards do not have to be removed as some would tell you. (Read other 'How to' posts on this forum). When the whole mirror is off sand the base to remove all the blistering, mask up and apply a good coating of ETCH primer. For my Zed which is Montreal Blue, I did actually get it made up at H**fords, and to be honest the match was spot on as you can see from my photos. A lick clear laquer to finish it off, and jobs a good'un!
A word of warning, Do not force at any cost or it will probably snap on the weak shaft! (£70 is the going rate for a second hand mirror, if you are lucky) Be very patient and try and soak the inside with a spray of WD40 or such like. Hands up, I was that impatient fool!
Definately a job worth doing
Pete
