Hello,
The rubber band sealing the glass to the reflector cooks and seize the glass on the reflector.
You can separate the glass from the reflector by destroying the rubber band.
You can buy a new one at every BMW dealer P/N : 63 12 1 353 623 for less than 8 euro.
It is a /5 P/N but the same as the R65 one which is not listed on the fiche...
Edit : It is NOW listed for the R65 P/N 63 12 1 243 595 and cost 14 Euro.... I've always used the /5 version...
Edit :
I use talcum powder on the rubber band and it seems to prevent it to stick too hard on the reflector...
Refrain to remove the center light protector otherwise you will blind incoming traffic...
And do not ask how I know...
Do not break the glass... It is available (P/N 63 12 1 243 541 ) but cost about 100 euro apiece ....while the reflector is at 175 euro each

All that make for a very expensive headlight !
You may find lower prices at a Bosch dealer if you can find the Bosch P/N ...