Good to hear you got it all fixed.
For posterity, when the plastic thermostat on my M50 cracked Northern and I changed it out in a Wall Mart parking lot in -15 weather, but that's another story. One of the bolts broke off like the OP's; I put some sealant on the new used housing, put it together with the remaining 3 bolts and filled the coolant. It's been over 3 months and not only did it not need to be bled at all, it doesn't leak a drop of coolant. True story.
What's the difference between a BMW and a porcupine?