On my first '03 I had to replace one of mine due to condensation in the lens. The parts guy gave me one under warranty and asked if I would just return the bad one when I switched it, which I did and after that it was O. K.
Previously, my '01 2500 had water drip out of the trip computer which was also the result of a bad light/gasket.
Therefore when I ordered my second '03 I specifically did not get the cab clearence lights since my previous two experience's with them were lousy. However, I know you guys have 3500's so you had no choice.
If its any consolation both Ford's where I work have water in every clearence light on the roof.