Since having the Eriba I had noticed moisture/condensation int he rear light lens, but only on the one. As it had not effected anything I left it but have now taken tout to have a good look. I can't see why.where the water is getting in. The rubber O ring around the bulb holders seems fine. It's only happening on the one lens all other 5 are fine any clues from anyone here. There is a little play in the black plastic when slotting it back into the Silver trim but all feel exactly the same.

I think the answer may be to drill a very small hole in the lower part of the lens to allow for ventilation, my Land Rover freelander has these very same holes in the lenses of its rear lights.

Thanks but I would prefer to find the source of the problem and rectify it as it started with condensation but when I took it apart I poured out water that was boy 7mm worth sitting in the lens so it is getting in somehow.