Hi Marty,
Sounds like the notorious "Amel stern squat" may be causing water to pool in the aft portion of the vent compartment - often exacerbated by "stuff" on the stern (arch, davits, outboard in rear lazarett). Add 10 shots of anchor chain forward and see if it fixes it. 
Craig - SN68 Sangaris, in Oriental, NC "the sailing capital of North Carolina"