I'll be interested to see what the experts say, but I think you're only option is to replace the tumbler. Not easy, from what I hear. Had to have it done on my 92 when AAA dude broke key in lock.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife