Passenger side mirror will operate up and down from the switch but sometimes will only adjust out, next time it ign is turned on that may change to up and down adjustment still but will only adjust in .
As said never got around to looking at it but just noticed that when the operation of the mirror fails when pressing the button, (either in or out) the dash lights come on everso dimly.
My powerfold upgrade from Paul will not have any impact on it as i provided a separate harness from one side of the car to the other when i installed it, and anyway the fault seems to be with the glass adjustment not the powerfold action.
I have changed the switch assy for another one and exactly the same happens so that can be excluded.
I suspect the harness connections by the doors suffering from water ingress/corrosion, unless anybody else knows better.