today while my mini was gettign a new clutch i asked about the third brake light leaking water into the vehicle around the battery. from what i understand this is a very common problem and they do a gozillion of them every month. I had it replaced but i asked why it leaks. i was under the assumption that its a gasket behind the light that wears out. he said that i was partially correct. The mini tech stated that it leaks for 2 reasons, 1 being the gasket and 2 being that when they are put in that the screws are overtightened and it pops the red outer section off the light. BE CAREFUL do-it-your-selfers. dont overtighten! noone wants to spend money and have to re-spend. He told me alot of times people will install one themselves and it will either immediately leak or develop the same leak problem over time from being pressed against the body separating the 2 sections.
hope this helped someone out there, i thought it was great info.

 

Good to know. Thanks