...and finally, Esther (if you're of the age most likely to be driving a 75, you'll know what this means): the brand new o/s mirror has started to malfunction. When it opens out, the motor keeps running.
What this means is that - for whatever reason - it isn't opening quite far enough to activate the internal microswitch which cuts the power on completion of the turn.
Bashing the mirror with a bottle full of water both stops it and is satisfying. However, the end of this sorry saga with one of the worst-designed mechanical objects I've ever encountered is that I have finally admitted defeat and disconnected the powerfolds permanently.
Good luck to anybody else who tries...