Guys, I see this posted sometimes, and there's a big factor here: OEM vs remakes/aftermarket on gas caps. Mopar caps from '70+ were partial-pressure caps, if you read the Allpar article it explains it better. The thing is those were only used on OEM caps. If you buy a remade cap/aftermarket cap those are all just vented caps. Way easier to remake them that way as that's whats readily available. Go investigate and see for yourself - even the primer exact replica caps are vented.
