Could you have a leak in your water heater or galley sink plumbing (lose
whale fitting/split tubing)? That could be sending water into the area you
describe? You could add some food coloring dye to your water holding
tanks, and over a week or two see if the water under your galley
floorboards is that color. You are in a cold zone, so something could have
gone awry with wintering your plumbing. Just a thought. I've also had
whale fittings under the galley sink split on me from just the water
pressure as they aged.
-Christian 1994 C320 #138 "Canuck" Monroe Harbor, Chicago, IL