check engine light.....valve covers leaking?

7speed

So I took the car to the dealership because of check engine light. I think it was throwing misfire code.

Per phone convo with service advisor. (Seems like a new guy never seen him before) my valve covers are leaking and thats why throwing code. He was saying good thing I have extended warranty so instead of $1000 (whattttt) I pay my $100 deductible. He also said there is a TSB for 370z and GTR but he didn't know off hand for what but they will be doing that also for free of course. (Only thing I could think of is steering lock)

Two questions/concerns?

Only reason I could see valve cover causing check engine light is fouling plug but more importantly shouldn't this be covered under 5yr 60k powertrain warranty? Car is 09 with 48k. On a side note they replaced short block back in January, could they have done a shitty job at that time and be related?

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09 370z 6spd traded 1/12/15 for 15 Challenger RT 6spd