These G body cars run the metal fuel line from the tank and into the inside of the frame at the crossmember. Often the line rubs a hole or rusts through in that area. Mine did.
You probably can't get to it to put a hose splice over the hole or install a union,
so what I did was run a new steel brake line from the tank to meet the line farther forward and connected them together with a brass union.
Replace the rubber lines on the top of the tank while you are there. They have a lot of years on them.