My head gasket experience is with a M104 engine, 130k. The engine overheated with a failed thermostat and 2-3 months later I had the first signs of oil in the coolant tank. The repair was about $1700. Add more if your water pump is about due. My tech said fixing this sooner is better than later as the oil deteriorates all the rubber hoses in the cooling system.

glenmore
1991 300CE
1990 LS400
2000 C280