Have you checked the three wires on the passenger side switch? I have a distant memory that when it was wrongly connected it caused problems but can't remember what! I know that if one of the wires was disconnected one of the door switches didn't function. Worth investigating perhaps if you haven't already.
Do you have a wiring diagram? I found some quite good ones somewhere and leave them in the workshop manual whenever the car goes to the garage, saved them quite a bit of searching sometimes. I could scan the relevant one and post it here if that's any help.
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