Rubber seal go dependant on enviroment factors, cold,hot,wet,dry etc. Yes you will have to have the glass removed and new seals fitted and the seals I would say from the dealer.
On my model there are two small rubber pieces around the rear door which crumble, mine hasnt as its always been garaged, although my mates car which is 4 years newer than mine have start to crumble, on going to a BMW meeting some of the 7 series didnt have any rubber left, so its all down to how you look after the exterior and where its kept and the major factor the climate you live in.
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