If you are talking about a gasket around the plastic, I have no idea, but I bought some rubber "o" rings and stainless steel screws for my running lights. A few folks have had this issue, but mostly from the screw not the casing itself. The "o" rings seem to work.
Computers manufactured by companies such as IBM, Compaq and millions of others are by far the most popular with about 70 million machines in use worldwide. Macintosh fans note that cockroaches are far more numerous than humans and that numbers alone do not denote a higher life form. -NY Times 11/91