I replace the Fuel Filter at service time. Part is only £20-£25 so its cheap enough to change, only prob is VW say it doesn't need doing, ITS A FILTER!! Anyway, its a 10-15 job, my VAG specialised does mine for £40 IIRC inc the filter, part number was
1K0 201 051 K but came across another one which i think is the newer one, being
1K0 201 051 C.
If your car is an early GTI then it will have a Revision C Diverter Valve so go with either a Revision G (diaphragm version, the latest flavour) or the Revision D (piston type). I read somewhere that the k03 benefit from the D and the bigger K04 from the G. No idea if that's the case though. The revision G does seem very good on my Edition 30.
Revision D
06H 145 710 DRevision G
06F 145 710 G