Cleaning is always an option; however, if it is the original tumbler for the vehicle I would highly suggest ordering a new one. I myself just completed removing the steering lock from the column, which is a feat well versed on the boards. If the tumbler gets bad enough and will no longer allow the key to turn to the "ON" position you have to either drill out the tumbler or remove the entire ignition lock from the column.

Unfortunately, my local dealer informed me Mercedes no longer keys tumblers to the VIN and the new tumblers come with a set of two new keys. New tumbler with set of new keys came to ~$96.

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Roy Brake
Fort Worth
1980 300SD
1987 560SEL SOLD@216K