Well, I just told them my car has been pinging when climbing uphills or during hard acceleration and I said that they better check the timing or my engine is gonnna wear out prematurely. So they checked it for free. My dealer is pretty cool. You just gotta make it sound like it's a car design problem and not due to everyday use. I think the timing issue is well known with Nissan so I'm sure they'll look at it for free. The mechanic that fixed the timing said it happens to a lot of Nissans and that the computer mucks with the timing. Use that angle and they'll most likely fix it for you free of charge. Good luck.