Just a wild guess... But there's a chance the end under the hood goes to a canister full of charcoal. You'd have to open the inspection hatch that lives in the front US passenger side wheel well (on the rear side) to be sure. Don't remember if that panel is secured with screws or pop rivets.
If I'm off target on that, hopefully someone more expert can steer you right.
If, in the one case cited, the problem is a cracked rubber filler hose between the filler neck and the tank... new ones can be found from Greg Gordon at HPSI. Those were NLA for a long time. But we convinced him to tool up for a production run. His units are for GTV6s, which have different diameters on each end. Alfettas have the same diameter on the filler neck and gas tank port.