Just aft of the rear axle is a rubber hose connecting a break in the steel fuel line. It is where the GM fuel line ends and the Barth fuel line starts.

Do you know how old yours is? Do you even know it's there?

Mine sprung a leak on a trip recently, stopping me dead. I was particularly annoyed, as I did not even know the sonofagun was there. Had I known of its existence, I would have replaced it when I replaced all the other old hoses. Had to cut off the tailpipe to gain access, as the hose was buried inside the flanges of both the frame rail and the crossmember.

Note: This is for sure on mine, but as all Barths are different, your results may vary. Since Barth put in their own fuel tanks, I would expect other Barths to have a similar set up, depending on how far aft the fuel tank was mounted..