I have seen this a number of times. The fix is this. Take off the blade. Then take off the plastic cover on the top of the transmission. (This is the black cover at the base of the blade).

Now clean and lubricate inside there.

(At the dealer, they replace the whole unit for this)

__________________
Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS