I had a similar problem on my '93 CE. Some moron tightened the lug bolts so tight that 3 of them broke off in the wheels. It took two of us all afternoon to drill them out. I then had to go to Mercedes and buy 20 new bolts at $6 each. What really ticked me off was the original bolts were the double type, that is the head of the bolt was flush with the face of the wheel.
Apparently Mercedes no longer offers these.
Anziani
'93 300CE 180K
'95 E420 117K