Tried all of that already
I even replaced the stern rub rail last year. This was a big job I must say, however I'm glad I did it. The lower part of the rail sits underwater when under power, and I found the beginings of delamination behind the rubber. It's interesting how the deck and hull are joined insofar as the hull is "finished", and the deck is oversize of it. They then trim one mold part to fit the other's contour. The problem is that this cut edge is unsealed, and water gets in. Beware. Potentially large problem.In any case, I have hung upside down in this locker for an hour or two, trying to isolate this leak. What I do is dry it completely, and then lay in dry paper towels. This of course is on a dry day.Sure enough, after a short while, there's about 1/4 inch of water around the forward partition of the locker at the juction where the partition meets the hull. It is defintely not dripping down the hull, or coming from the rub rail, as the rail is out of the water at that juncture.My opinion is that if it were a small hull leak, I would get the transom considerably more full than the 3-4 inches that collects. I've also considered the exhaust, although this happens when I am inspecting it with the engine off.I was thinking, maybe it's a leak in the fresh water system somewhere. There is the one FW tank on the starboard side aft.I should add, I'm very handy on boats, and there's virtually nothing I cannot diagnose. This has been a very confusing saga.In any case, I've solved a lot of other 40.5 owner's problems on this site. Maybe someone can now return me the favour.