Can't recall if I shared the boat story or not. It was unused for approximately 5 years, stored outdoors in Buffalo, uncovered, under a huge freeway overpass, accross a small canal from a Cheerios plant. So my guess is that the crap in the air settled on everything and in between rain/snow storms which would have washed it away, mixed with dew and turned into some sort of concentrated yick that dripped slowly out of the cockpit scuppers and stained the hull an ugly brown. The stain is only about 1" wide but goes from the through hulls down to the waterline (about 1' long). Oddly enough, these two stains are the only ones on the entire boat. The broker assured me that they would buff off, which of course they did not. I have tried cleaner/wax, polishing compound, rubbing compound, acetone, laquer thinner, CSR and softscrub with bleach and have not made a dent in it. Now that we are out for the season I can work on it again. I know there has been discussion about removing spider poop, bug guts, black stains and so forth, however this is none of the above and very stubborn. I would prefer something chemical although I have been pondering 1000 grit wetsanding?