F I X E D!!!!!!!!!!
Finally.
Removed the gm3 module and it was really covered in dust. One of the relays (I'm assuming it was for the power windows) had some corrosion on the solder.
Cleaned it up, put it back, and nothing. Until I messed about with the button loads of times and then all of a sudden it came to life and the window is now working perfectly.

So corrosion on the gm3 module was to blame. Also corrosion in the wiring harness on the door pillar to blame.


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