Well the internal light switch is fixed. You pop off the clear cover from the front and then undo two T20 torque screws and the whole assembly pops out. A slight tweek upwards on the embedded contact and a bit of vaseline fixed the switch problem. I also read that if you fir an assembly for a MK4 Golf it has the same plugs and fits. This will give you independent reading lights for each side and better overall light level. They are only £15 new so I will get one and try it.I think the door switches are magnetically actuated.
But yes, as you've clicked with, central locking does depend on sensing all the doors being fully closed before it can work. If you are lucky it may just be down to adjusting how tightly the doors close! Need some 12-square sockets for that, not torx, FYI.