Here's the usual culprit - -
- - which leaks if it's not fitted correctly - this usually happens after someone's been into the tank to fit the orange clip - your 2004 needs one (or has one). There's only one way up for this seal and it must be fitted around the tank port before the filter or pump module is placed in position. There's lots of info on doing this so ask if you need help.
HowTo: See last section in here:
https://www.the75andztclub.co.uk/for...ead.php?t=9108
TC