Replaced the thermostat, flushed and filled, and overtightened the bleeder screw and it broke! It was incredibly corroded and the head just tore off--I didn't think I put that much pressure on it.
I also found out that the bleeder screw cannot be purchased on its own--------it is part of a $70 larger assembly----------any place I can get just the screw?

 

E39 5-Series Cooling System Parts

 

AWESOME! That works! I'll go to the local BMW dealer in the morning

 

based on my experience, buy three, you will need them. they break pretty easily. I had one crack in the middle, couldn't see it. Only knew it had the crack when coolant was all over my office parking garage floor. Keep the extras in one of he dash coin drawers, the occasional rattle will give you a sense of security. Trust me, I learned from experience. Phil