Due to wear, high usage vehicles can experience ignition lock and tumbler failures. The ignition lock cylinder will generally require replacement to correct this concern.Google+
Car Problem Reports
Mercedes-Benz C280 High Usage Vehicles May Experience Ignition Lock and Tumbler Failures
Mercedes-Benz C280 Problem
Average Mileage: 142,390 mi (67,000 mi - 250,000 mi)
Visitor, 1994 Mercedes-Benz C280, 121,000 mi
the master key was worn and causing tumbler failures .. I started using the round key instead and it is still working
Visitor, 1994 Mercedes-Benz C280
The key wont turn on the ignition, I guess I'm having the same problem, as the other people!!
Visitor, 1995 Mercedes-Benz C280, 67,000 mi
drivers side doors lock no longer functions, have not yet replaced
Visitor, 1997 Mercedes-Benz C280, 250,000 mi
Key won't turn. But after several tries turns and starts car with no problem.