Petroleum jelly isn't good on a lot of o-rings, it degrades them. Won't matter on urethane o-rings, but rubber and nitrile you shouldn't put it on. It's not a great lube anyway, that's why petroleum based greases don't often get used in the paintball industry, you get a lot better properties from most of the synthetic greases. In the case of the Ion, I'd be willing to bet that the reason why the Vaseline is working better than paintball grease is that you were either under or over applying. Buy some Dow33 and some synthetic oil (ACI and KC are both good) and you'll be better off. Avoid petroleum based products, like vaseline and mineral oils, and absolutely DO NOT use any penetrating oils, like WD-40 or TriFlow.
