I have had a similar problem with the cabin aft port locker under the bunk. I also think it was the cockpit locker lid. The carpet showing behind the shelves was dry, if a winch leaked, I would expect to see some damp there.
The boat sat on it's trailer for the winter with a portside list, and I am ashamed to say I hadn't kept the channels either side of the lid as clear of muck as I should have done. Up to now, I have never seen a drop of water inside the boat. Some water drained to the void at the back, which I have attempted to empty with the bilge pump, but I think more may have gathered between the hull and the inside skin, since after a sail (involving heeling to port), I go another lot of water in the locker (not salt, so rain water). There is a hole in the top aft corner of the locker, planning to stick a siphon down there to see if I can get rid of what is left, then look for a gust on starboard tack!
Jim Hamilton
Sandy Lady