We had a very similar problem with our World. There was leak between the bailers and the double skin. If you tricked water from a hose into the scuppers it disappeared inside the hull at a rate of knots! So if rainwater got under the cover the bilge water was fresh on the other hand on a wet sail we could pick up several gallons of sea water. Ian Porter sorted out the leaks for us. Good luck!
Nick 9922 LizzieB