Some PO of our sailboat changed out the Atomic 4 gas engine for a diesel. Used the same fuel tank. Disconnected the 'Gas' deck fill which was next to the tank vent on port. Added a 'Diesel' deck fill on the other side of the boat, left the tank vent on port.
Happily, no one put fuel into the disconnected 'Gas' deck fill before I foamed it full. Filling the tank requires the admiral watching the vent while I'm busy on the other side of the boat.
Must have been a reason to drill in a new fill rather than replace the cap or the fitting.