Cheers Chris, I think the issue is more to do with the carburettor which is being looked at later. I must be honest I don't like the idea of a leaking carburettor. When you say staining did you mean painting?
Got around to removing my fuel tank on the weekend., and had alook at the fuel tank vent pipe. 2 bloody great kinks in it where it passes through the chassis rail & up through the floor towards the filler . You can see in the picture they're pretty bad. Hope yours looks better with smooth curves.