Before:
Beth's Trunk Lid Brake Light (leak, water condensation in trunk)
Beth writes:
Old Light with Cover
Brian W writes:
Regarding the third brake light be aware that after that area is disturbed, unless the person is very careful, the gasket can easily be compromised. It can be as simple as a speck of dirt caught between or rolled over at an edge.
The good news is that it usually doesn't have to be replaced. Just remove the brake light with a Torx, T8 I think. Carefully clean the gasket and the surface around the outside of the brake light and re-install. Listen for a "click" when the two separate plastic pieces snap back into place.