Had a simular failure on my 07 GSA at 84K in Oct. Covered by an extended warranty. U Joint broke, and drive shaft jamed in the housing. Was at speed when this all happened. Strong vibration and loosing speed. Stopped the bike and it would die in gear. OK in neutral. 100 miles from home, very limited cell phone coverage. Walked about 1/2 mile to find a few square inches that the cell phone would operate and called the wife who came with trailer to retrieve bike and me.
When the dealer disassembled, reported some play in the FD and ended up with an entire new FD, the updated housing with drain, along with driveshaft.
There have been simular failures on previous models. Paul G had written an article a few years ago on this very subject, checking drive shaft u joints. Had them checked on my 01 GS at 102K and they were beginning to tighen up.
They are not a seviceable part and will require some inspection as the miles accrue
For a dealer to say they "never seen this before" or something like that, I think is a poor excuse.
Glad that BMW is covering your failure