Hello,
my 54 has a similar prob. I found out it was condensation forming on the inside of the metal roof. My roof is now bare metal, so I my plan is to insuluate the entire roof, then put in the new headliner. If I were you I'd get on it, becuase I left mine go for a while and now i have rust bubbles on the inside of the cab from the condensation.
Hope this helps you. Gman.
