I do a fair bit of driving on gravel roads in the 'Bird, and I always get dust in the tails...
I've had 'em aparts 3 times now for cleaning, and this last time, I used copious amounts of silicon goop to seal em up with, but they got dust in em again.
What else can I do, this dust is for the birds!
Mine have dust in them, but I know for a fact that on one of them, the lens is halfway separated from the backing part, so I figured the dust was from water getting in them. I was gonna try to seal them up but never got around to it. Kinda glad I didn't do it now!