David,
I'm just taking a stab in the dark here, but possibly it's the hose that  the 
pennant for the centerboard runs through that's leaking. It's held on by  
clamps and they can get loose. The only way to find out is to tear everything  
apart and visually check. It will become obvious once the floors are up. There  
are very few instances of the cap actually leaking, but the hose is a comes up 
 more often than not.
 
Rummy