Bob, I've had the same problem with a chainsaw, and soon found that the only solution was to replace the grommet that seals between the tank and the fuel line. I bought a grommet and fuel line together as an aftermarket item. It fixed the problem and was still perfect when I gave the saw away a few years later. If you take the tank to a mower shop (preferably not the one that tried to fix it with gunk) they may have just the right part within arm's reach of the counter: they certainly did for my obsolete and unusual chainsaw. It didn't cost much, either.
