The present windscreen is actually in good condition, but the installer thought that the condition of the car "deserved" a new one (and he deserved the additional profit?).

Hopefully the "old" one will reinstall without cracking (in its new gasket). I was told that glass with considerable UV exposure gets very brittle with age. Is this true?

Bob
Whatever you do, do not buy a non BMW glass, they just don't fit right. If your's is a BMW glass and sandblasted, it is still worth more than a new after market one. I bought an after market glass, and I threw it away after a couple of months to replace it with a good used BMW glass after I re-painted my CSA. I believe the real BMW glass is around $500 and you should inquire from Paul at Maximillian.