The simple answer to your problem is that your motor is (was) burning oil. This is a very common problem with these VQ engines. In fact, on my last G35 I was on my third motor. All of them burned more than a quart every 1000 miles.
Even my current 370Z burns about a quart every 1,000 miles.
The dealer knows this but is trying to play ignorant.
Check out my post I wrote on August 6, 2006 on G35 Driver
Everyone: Check Your Oil! - G35Driver.
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