Thought Id include some pics:
This is a wheel off task IMO - makes it so much easier.
Remove 7 screws (yellow arrows) and one really "stupid" plastic expanding clip (red arrow).
The plastic clip just pulls through but is damaged in the process. I replaced it with a better clip with a hammer in, screw out expander.
Pull back the wheel arch liner and wedge it behind the brake disk - giving lots of room to work.
Remove electrical connector and bulb from back of foglight unit.
Two clips hold the back on but allow it to rock - controlled by the adjuster on inner upper side.
Press open the clips gently to allow the back to come out of the rest of the light unit. Swing the back over the the inner clip so that it then lies to the inner side of the light module. Slide the two pins on the adjuster upwards and backwards out of the adjuster bracket grooves. (5 &6) The back is now free.
Clean and dry the light module and the back.
Clean the rubber O-ring (green arrow).
Replace in reverse order.
The mirrored finish had come off the inner surface of the back so I sprayed it silver but IO will get some spray mirror finish and do it properly.