Willie, if you can actually see a leaking gasket, then you are lucky.
I suggest you take out the tank and clean and inspect the top. There are
seven or so fittings there that may leak, and there are excellent spots for
rust. I replaced my tank after discovering that the top had turned into a
sort of metal blotting paper. I could see the petrol soaking through it.

Good luck

  ************************************************************
    Johan Nyberg, Sweden N 59o E 17o 25"
    '86 Caravelle C
  ************************************************************