The odo has a small gear that can slip on the shaft that it drives. To repair it takes either a very good tech or a speedo shop. (I do these in house on occasion with good luck but I have experimented a great deal with them to get the repair done right)

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM