Hi Karl i was just answering Pauls question id say yours is the key battery and for the price of the battery its worth a go if it hasnt been done.
Problem with mk4 platform door control modules are they are individual to each door hence one can be not working and others fine. At the same time it can work and then not work as a lot of the time it is a bad connection caused by water, solder breaks etc. If one day it wasnt working I could tap the area of the door near the module and it would work again. It gradually got worse over a few weeks/months untill i replaced it.