You have a very,very slight weep.So slight that it doesn't drip,but slowly dries,hardens,and turns to varnish.That sticky stuff is varnish.
Vangogh - agree, it's not uncommon.
Your leak could be coming from one of two places:
--- Connection where the shutoff valve screws into the tank (the more common), or
--- Leaking shutoff valve with fuel leaking out of the valve body.
As to how to fix it, you need to drain the gas tank (I hook a plastic hose to the carburator end of the hard line from the sediment bowl to the carburator and run it to a gas can placed in front of the radiator), disconnect the line from the shutoff valve to the sediment bowl, and unscrew the shutoff valve from the bottom of the gas tank. Once you have the valve out clean up the threads on the valve body and in the tank (someone in the past may have put some sort of goop or thread tape on the threads), coat the threads on the valve with a fuel-proof thread sealant (do not use thread tape or thread adhesive, you need a thread sealant - I use Permatex 59214 High Temp because it's what I have, but Permatex 56521 will work also), and thread the fitting in. Don't wipe the connection, let the stuff bulge out a little bit at the base of the connection. Reconnect the inside fuel line to be sure you have it lined up properly, then let the assembly sit a couple of days so the sealant can set.
While you have the fuel valve out, this would be a good time to install a pencil filter if you don't already have one (
fuel tank filter screen as an example, all the normal suppliers have them).
If you have the threads sealed up tight and still have the leak, it may be coming from the valve itself. Leaks through the valve usually are apparent when the valve won't shut off fuel flow completely. I've had poor luck with the rebuild kits offered for the valve, and have just replaced when necessary, the repro valves i've gotten seem to be decent quality. Install/reinstall per the above.
JayJay
