Re: Fuel Tank
(I'm assuming that your P30 has the original A4 and tank.)
P30s came with monel fuel tanks that will outlive us all. Don't replace it. You can't remove it without pulling the A4. That's a fairly big job (I did it on my P30), so you'll have to try cleaning it out through the fill hose. Try a solvent, maybe acetone? Most importantly, change the fuel filter(s) early and often until you have confidence that the crud is gone.