Here is a post regarding the brake flange. From 12GS Rear Disk Flange Cracks?
Originally Posted by hancockbs
BMW seems to have gone to a third version of this flange. It now comes in two parts; the flange, which is about 60% as thick as the original and a spacer ring, which is not heat fitted. The flange appears to be steel now as well.
I received it from Countryside BMW on Friday. Total for the two parts, plus five rotor bolts and shipping was a bit less than $300. I installed it yesterday. It was very hard to get on. I used a lot of ice to keep the axle cool while continually heating the flange and it went on a tiny bit at a time. I am concerned about torque values now. I don't know if they are different for the new flange design. If I can get a good answer, I will post it.
It was also pointed out by a sharp eyed person that the wheel holes on the flange might be cracked. After cleaning it up a bit, I found that all five holes are cracked. I guess losing the rotor at low speed is probably the BEST thing that could have happened here.