When H-D went to the small "bullet" turn signals, they changed the design to what we call in the auto business a "wet" design. The old signals had a gasket between the lens and the housing; the new ones have the gasket inside between the socket and the housing. If the lens is seated and not broken, the amount of moisture that enters should be insignificant and will burn off quickly from the heat of the light. That's the theory, anyway. The problem with that theory is that moisture can still get between the bulb and the socket, and in the case of the rear (non-running light) signals there is insufficient heat produced to dry them out. My suggestion on this type of light is to coat the bulb with a heavier than normal amount of dielectric grease to form a seal right at the entrance to the socket.