I burn about 1 qt. in 1000 miles, and smoke at high RPM. I ran a compression test and I got 180 psi in all four cylinders. I guess I can do a leak down test? But if the compression test came out good, does that narrow it down to where it's burning oil? The motor has 170k miles, it's a SNC, 1990 and I run Vavoline 20w50 syth blend to cope with the burning oil.