Sorry Schtum but I can't help with the technical side on this one.
Have you considered approaching BMW as the gasket had been incorrectly installed? I assume your bike is out of warranty?
Back in the early 80's I had a 750 Bonneville which lost power on one cylinder. Stripping the top end revealed that the circlip hold the gudgeon pin in on one piston had never been fitted resulting in it sliding out and severley damaging the bore. The bike was well out of warranty but I sent the parts to Triumph for examination. They agreed with my findings and sent me a new set of barrels, pistons and all relevant gaskets.
You never know, it may be worth a try?