My BAP petcocks were about 20 years old and the rubber gasket got hard and set after a long period.
They began leaking so I replaced them with some similar, but with plastic handles, from Eurotrash.
I made some cork replacement gaskets for the BAPs and they now seal well.
The ethanol based gasoline sold now affects gaskets and seals and sealers. Check anything in the fuel flow system for deterioration; filters, valves, hoses, and gaskets. Also steel tanks can oxidize and rust particles will pass through many fuel filters and accumulate in the carb bowl.