It is not coming from the main filler hose that goes to the tank, it appears to be coming from a yellow plastic bit which clips into the top of the tank, next to the main filler pipe.
Here is a pic of the bottom, it is coming from the other side of the yellow clip thing!
It doesn't leak if the car isn't running.
Help?! Cheers.
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1998 GTi6 Bianca White