donbrew

Not really an O-ring it is the rubber wrapped around the nipple. Anything (except silicone) that will make a good seal and stay that way.
Don't use silicone anywhere there is any chance that the out gassing from it might get near the catalytic converter. Even remote chances like this.

greg8453

Those type fittings are plug and play. Just jam the hose onto it and it's done.

Oldblue

Dealership won’t have it, you can wrap Teflon tape around the nipple to seal it up.
You could go into local pic a part

donbrew

This thread is about the Vent valve.
The Purge valve is under the hood, it allows fuel vapor to be sucked into the combustion chambers. The Vent valve allows air into the fuel tank while blocking the fuel vapors from escaping into the atmosphere.