Hi Biffo, if you undo the 2 cross head woodscrews and remove the mirror completely, turn it over and you will see a hexagon 'hole' into which you can put an allen key of the right size, and gently tighten it, clockwise, it won't need to be turned much - DO NOT OVERDO IT, just enough to hold the mirror in position.

Easy. Good luck.


Paul
[At last, I have a car I can polish]