I had to remove my tank + change fuel filter , so i syphoned the petrol ( or what i thought was petrol ) into a jerry can . jerry not quite big enough so i used a clear plastic container , when i had finished i noticed that fuel in the clear container didnt look right - half a pint of water time to check jerry can . in total 3/4 of a pint of water . petrol cap removed drain hole checked / clear , so have replaced gasket & cap with a smear of sealent !

It may not be anything wrong with the gasket.
Because of the design of the filler cap, when it's raining, the water sits around the cap. When you open it the water goes inside the tank. This may be a small amount but if repeated for many years, at the end it could add up to a substantial amount.

ouch archie ......that could have been fun on a trip ...or a few years later after the rust had set in ...

good find

It was just luck that my jerry can wasnt big enough , and i had to use a clear container , other wise i would not have noticed & just pored it back in !

Once in a while I suck out that liquid from the corners of the tank. It also helps getting rid of any dirt particles sitting there. Especially if they're metallic particles they'll cause rust sooner or later...