That is a somewhat common repair on a variety of Mercedes vehicles. A soft drink or coffee finds it's way into the shifter and kills the module. When that happens, the shifter usually gets replaced.
Derek is correct in the fact that it will require a Mercedes (in this case properly equipped Chrysler) repair facility to program the shifter to the car. Until the car is formally introduced to the new part, you're not going to go anywhere.
When I took my SRT into our shop, the only two systems we could not get in to was the ESP and shifter. I had one of our Mercedes shop foremen working on it and that was as far as he could get.
If that wasn't a mistake by my tech, then you may have to go to a Chrysler shop and skip the Mercedes guys.