I took both my rear lights off a few months back after noticing so much condensation forming that there was a small amount of water gathering in the unit. The fix was to remove completely including the lampholders etc, empty water out and use a hair drier to dry out the internals followed by drilling a small hole in the underside out of sight to provide an exit for any future build up... it worked a treat as I cant say that I have noticed it return since..

Ive had this problem on the Fatty for a while, did a search on here got out the Black and decker and a 3m drill bit
and Happy days problem sorted  2004 vogue
1978 Pontiac Firebird
2010 Fiesta

+1 from the wetlands of Netherlands Mark Offringa
Utrecht Netherlands


2007 L322 / 3.6 TDV8 / Vogue / Java black
2002 Mini Cooper / 1.6 116 hp / Red + white roof / the magic back-up

Gone:
2002 L322 / 4.4 V8 / Vogue/ Adriatic blue
2000 Audi A6 / V8 4.2 / Brilliantschwarz
2003 L322 / TD6 HSE / Adriatic blue