DEM900

Mine is  saloon, the nut has screwdriver slot and spanner or socket flats, the nut is not the problem it is the locator pins that stick in the rubber retainers

Hi from a newby, just wanted to share a little trick to remove the rear lights of the C6 A6 which can be difficult to extract from the securing pins in the rear wings, Audi advise using a plastic tool to help the lamp free from the locator pins to avoid damage to the paintwork around the light edge, however this is not always successful as the pins tend to stick in the rubber retainers in the wing, so the trick is to use special tool STR-I-NG available from just about anywhere. See below.

When the retaining nut has been removed the lamp can move outwards a small amount, this lets a piece of strong STRING be threaded behind the lamp starting at the boot aperture, simply thread the string around the lamp from top to bottom, tie a strong knot in the string at a point 6 inches past the lamp, insert a screwdriver or  bar through the string loop and pull, the lamp will pop out without any damage to the paint or lamp, before refitting smear the rubber  retainers and pins  with silicon grease which will enable easy removal next time a bulb blows.

For those who knew this method sorry for the repeat, for those who don't it works.