I had a Vette shop replace the intake manifold gasket on my '90 L98. It began leaking oil again immediately and I took it back to shop, they redid the seal free of charge but told me it would likely blow out again due to excessive ring blowby and excessive crankcase pressure forcing the oil to push out the intake manifold seal. They noted that the pcv valve once again has oil residue in it despite having been replaced with the 1st gasket job. I had the shop perform a leakdown test--all valves were well within norm, and also a compression test--1 cyl 200 psi and the rest 205 psi at 101K miles. I'm skeptical--excellent compression, no visible exhaust smoke, not terribly high mileage with regular Mobil 1 oil changes, car runs fine--can there still be excessive blowby, or are they trying to cover for a screwup?