Federal Pump Leaky Cap

I have a federal pump with a “vented cap” and I am always cleaning up fluid leaking or misting out of the cap. It is the original cap from 1973. If I overfill it will definitely be found on the floor after a cruise. I have been just slightly under filling like just below the bottom line on stick to prevent spills but will still mist out of the vent though. I plan on going to a Saginaw pump soon