UPDATE

This x5 35i N55 doesn' have the B604 coming off the radiator neck...so odd.

Cap arrived, no change, still boils over.

Autozone had a coolant temp sensor, changed that thinking the sensor was reporting incorrectly, still no change. I think the coolant tank may be cracked and leaks under presure only...there are zero leaks untill it hits 102C+

Video of expansion tankHERE - you see bubbling from the evacuation hole, but it isn't coming from the cap.

ordering expansion tank now.