I got my '13 BRZ in early December. Only recently I noticed a small bit of moisture in the upper bits of the tail lights (alot of rain & snow melt).
I used black 1" gorilla tape as previously mentioned, and so far, after a pouring rain all day yesterday with excessive snowmelt on the car from the night before, there is no water in the taillights this morning.
Cheap & simple.
Ghetto? yeah...perhaps alittle bit. But I have the dark galaxy blue color and so the black tape isn't really THAT noticable anyway.