Advice on where to look and how to sort please.

 

what rear light? the third brake light? or fog in the tail lights?

 

I think he means the famous water in tail light mod. Search it its been discussed many times !! Or even go down this page and click the first one

 

water / condensation in off side rear assembly. how to access - lost handbook.

 

Search is your friend. Water and rear\tail light are good words

 

remove inner trunk liner... disconnect the bulbs.. drill hole in the bottom of the tail light... let air out... replace

your lucky im at school with nothing better to do besides being nice

NEXT TIME SEARCH!!!!!!!

 

or, if the car is new, go to the dealer and see if they'll replace it under warranty. 10 mins at the dealer can save you having to drill your trail light

 

Mine leaked in both like crazy when i first got it , I pulled light off cleaned it up , aired it out and then put silicone around where i seen the seal was sitting and drilled a small hole in the bottom , come time to take it off it will prob destroy the seal mind you but its been holding up for months of rain and car washes , not a drop of water inside .

 

There is a replacement gasket (improved) for the rear tail lights which fixes the problem. (the gasket goes between the taillight assembly and the car body)
The tail light assembly is vented into the trunk area so drilling holes is not required as the water will simply evaporate out once the leak is repaired.
It's not a bad idea to rinse out the assembly with distilled water, to remove any sediment, while you have it out.