Took me forever to find the screw as I have the same problem. I've managed to replace the switch but have the same problem.
When I press up on the mirror switch, the mirrors go down! They both go left, right and down and when the memory button is pressed the mirrors revert back and go to the programmed position.
So, the motors both sides work, I've replaced the switch with an eBay replacement. What else could it be? Mercedes told me that the star software won't reset them. I don't really want to pay £300 for a new one as they said they can't match the colour.
Anyone got any ideas?