I am SO glad this information was here.
Thankfully, my 540i6 does not yet have this rubber gasket issue, but my wife's X5 had some major issues with this rubber seal. I used realoem.com site to find the part number. Called BMW dealer and found that this part was updated multiple times and they were able to give me the replacement part.
It took some effort to remove existing seal, since some of the butyl seal for the windshield were stuck on the seal. Clean up also took some time. BTW, installation of the seal was very easy.
I did call BMW dealer to see what it would take for them to replace it and they gave me some outrageous cost for this ~$20 part replacement.
InCho - 540i6