Leaking fuel petcock

Not only does this common wear service item cause vacuum leaks, it allows fuel to leak as well. This one was found to not shut off fuel when no vacuum was applied (engine off)

The diaphragm has 4 small "cracks" that allow fuel to be "pulled" though and then it leaks out the vent

The best fix is OEM parts as seen in the pic.

Some will go cheap with aftermarkets parts, many of those do the job again right away when the new kit leaks, or do it again soon after when the aftermarket kits parts fail.

This OEM part lasted 19 years, so for $34 I bought and installed a new one..