If I may respectfully disagree, if that internal plug is missing the oil psi will be the same or even a bit higher (cuz the oil has a straight shot vertical up from the #5 cap to where it turns into the horizontle gallery & it ain't held back by the filter restriction) however the oil will be unfiltered (very bad deal) & if that ain't caught early on the eng will have an earlier(er) demise years on down the line while all the time the owner is thinking he is doing the right thing/being proactive with frequent oil/filter changes. We gotta find out what passage etc (something) that is being partly uncovered etc when it is running that ain't opened when bench testing with the primer. I'm thinking it is lifter related.