Hi Alex,
Have you tried taking the rear covers off and applying a beade of sillicone evenly spread and re-fitting covers. This nearly always solves condensated lights.
Regards,
Dean
I need 2x new bulbs anyway as they were getting dimmer and dimmer so I've ordered two decent Phillips ones.
I will try and seal them and see what happens but I think they could do with being split and the plastic being given a good clean so that the O/S matches the N/S.