The way the transmission cooler works, it would not be leaking into the boat. It would be leaking into the fresh-water supply which would then be dumped out the exhaust.

I do agree though, it would not smell like gas.

Your bilge use after a night of sitting on the water sounds VERY minor. Doesn't sound like gas is able to make it out of your bilge and into the water.

I'm stumped. Hopefully someone else can chime in with ideas....