Leak down test checks the valve seats and piston rings . Tell us more about these heads . Are they factory assembled . You may only have to change the seal that lifted . And the only ones that can suck oil are on the intake side . I think even if the seals lifted they still would act like umbrella seal that just move around on the valves . The old Chevy heads had just an O ring at the top of the valve . When the guides are new oil contral is not a problum . You need some oil so you do not burn up the valve stems .