I guess I can only say piston rings then, maybe valve. The vacuum increase at high revs could be sucking oil into the chamber. Under wot you should have a lot of bow by but since you don't go wot 24/7 you're probably not seeing a big drop in oil or filling the catch can up fast. At this point I'd go buy a compression kit from autozone for like $40 and test the cylinders and see what you get. The manual should post a range for healthy motors.
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13 370z-
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