I had something like that in my Scout, come to find out it was the gasket that was leaking from around the where the gauge sender in the tank is located......found gas, it had like you found in strange places that should not be. when the gas gets in the bottom it went from the aft to the bow through the water drains. I opened all access and poured water through it to try wash the gas/fumes out....after a week and the boat sitting the fumes gas seem to be gone. Dried it out everywhere i could reach, then everywhere layed newpaper around where i could get to to catch the first hint of gas leaking, easy to see than feeling with finger .. I agree on pressure the tank that how i figured it was the gasket....I filled it up undid all the fittings and plugged holes....no compresssor adapter to fit,,,,,so took it out in the full florida sun 98 degree's the tank presssured up on its own from the heat...It started leaking around the gasket.....Now yes it cost a lot to fill up, but its the sure way to get gas to flow out a pin hole in the tank itself, the other is pressure test it in a water tank look for air, of course that means removeing it,,,I dont know where Parker gets its tanks but 50% of all rec. boat aluminum boat tanks are build in Perry florida and i worked at one of the aluminum companys. They are tested very well and seen very few return due to a weld cracking, but it does happen from time to time,,I would bet and hope its just a gasket or hose.....