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 300E High Usage Vehicles May Experience Ignition Lock and Tumbler Failures
Mercedes-Benz 300E Problem
Average Mileage: 162,624 mi (102,000 mi - 194,872 mi)
Visitor, 1992 Mercedes-Benz 300E, 194,872 mi
Can't get key to turn to unlock steering and shifter.
Visitor, 1993 Mercedes-Benz 300E, 102,000 mi
Still trying to get ignition apart; key broke off! Lock cylinder spins around about 270 degrees but doesn't stop in the right spot to undo the cylinder lock! Now I know why I prefer BMW's! Removed assembly from another MB to use as a test fixture to get mine apart.
Visitor, 1993 Mercedes-Benz 300E, 191,000 mi
replacing ignition lock cylinder