Thank you for all the advice guys/gals. I am definetly not going to just drive it as is, if it can be avoided. As it sits now there is no stud sticking out to grab, it broke pretty much flush with the cover. I completely forgot about galvanic corosion. You would think that the engineers at MB would of forseen this problem. Right now it looks like I have a couple of options. Try to remove the other two and hope for the best. Then remove the broken stud. Then there is Lewallen's idea and buy a new housing. At least for time being the car is driveable, she has all the coolant she needs and all the clamps are tight. The only weak link is that thermostat cover.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section