To Frank: You can not reset the electrical limp mode with a generic scanner or any other "tricks" like removing the battery etc.
You will need a Mercedes HHT or a Snap On scanner with the appropriate cartridge and personality key.
A friendly dealer or an indy with the right equipment might be willing to re-set the limp mode for you

To JGL:
Did you ever check the Transmission Control Unit to see if there is oil in it.
If so, you can remove it, clean the PCB with a circuit board cleaning spray.