oh these light can be a right b&st&rd you have to remove the two size25 torx screws from the outside of the ar as you open the boot and then you will need to get a flat head screwdriver and from inside the boot shine a light up where the back of the lights show thro and push the really strong metal clips lose. you can use a plastic trim tool to just prise the clip off from the outside but i wouldnt use metal as this could damage the paintwork
if your still baffeled p.m me and il send you some pics!
back on topic my rearlamps rarely steam up but they have dome at 1 point fogs, headlamps, rearlights all steamed up