If you fairly happy it's not the pipe at the filler cap that's split, then you need to investigate further. It could be: The longer filler pipes, #6 and #7 in the parts diagram One of the little rubber joints on the breather system, there are two on the top of the tank, one in each rear quarter, above the rear lights. Tank to carburettor fuel pipes. Is your filler neck rubber definitely same as the one Pkrboo linked to on the samba? If so, it will be a straight swap for the one Jules65 linked. I've just looked at the Heritage catalogue, the diagram linked on here, you need to refer to the lower breakdown (the tank at the bottom) the top one is for early bays where the filler neck was further forward than late bays.