Hi, my name is***** problem will most likely be due to a faulty electronic gear selector module. When the selector malfunctions you will lose the gear indication on the display and you will not be able to put the shifter back into park. You should get the car connected to the Mercedes tester to read out the fault codes in the systems. I think you will find a fault code stored for the selector module. The selector module is the gearshift assembly. You will need to replace the shifter assembly in order to repair this problem.
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You're quite welcome.