Unless I'm mistaken, the small grey spot circled in orange is a vent which is covered with a super fine mesh which should keep out moisture, but I'm not so sure about that. The green line is where the front half and back half of the tail light are connected/glued together. The foam gasket only seals the assembly to the body and prevents water from getting in the trunk/rear panel area and should play no role in moisture getting inside the tail lights.
