i just had this same problem. time for a new tumbler. mb would never tell you its something to watch for, they make money on repacements and more when they are really worn. you are lucky the car is somewhere you can work on it. mine did this at home depot. i have heard the sander trick might work. i wasn't so lucky, ( although i did buy a sander and power inverter, no power source except the battery, to try that at the depot and returned it when it didnt work), i had mine towed to an indie and he did te entire replacement for a reasonable price. its nice to have work done at the stealer under warranty but hard to spend the money on a 13 year old car.

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1994 C280
2009 VW Tiguan
1993 Toyota X-tra Cab SE-5


1973 220D ... Gone, but not forgotten
1991 Alfa Romeo 164L Gone, wife MADE me forget it

2006 Hyundai Tucson... just straight out FORGOTTEN!