CLS500 W219 gear selector module fault

[ECain]

Hi, the gear selector module started playing up, at first I noticed that the Tiptronic wasn't shifting. Then pulling into the driveway I couldn't move it out of Drive nor put it into Park (obviously). If I turn the car off or take my foot off the brake it will move to Park.
Now it won't start, and if leave it for a while and it starts right up. The sensor must be detecting that it's not in Park or Neutral so simply does nothing. Took it to Mercedes and they confirm that the unit needs replacing or servicing.

My question: They say that the gear selector module is coded to the car, that buying a used one won't work as it's not coded to the car. If this is the case I have to go the expensive route, hoping not to have to do that.

Thanks for any replies