How can I regain use of the infrared remote door lock system? on 1997 Mercedes-Benz E420

My infrared remote door locks are not working with any of the sensors (batteries are not the issue). The plastic cover on the door unit has crumbled and gone away. I know the dealer is very proud of this door unit! Can I just replace the sensor in the trunk lid and gain access that way?.. or must I adresss the door unit as well? Thanks..

Asked by for the 1997 Mercedes-Benz E420