If my speedo gets enough rain (or if I don't pay attention when washing) enough water gets inside to fog the glass. I've sealed the edge with rubber(?) windshield sealant from the outside, which helped for a year or two, but the fog is back. Is this common? (My airhead had the same problem, if I recall.) Is there a better, longer-term fix? If not, how difficult would it be to disassemble it enough to put the sealant on the inside?

And yes, five minutes every two years for "good enough" isn't exactly a hardship.