Motor knocking. Took to dealership. After three days, they said they would have to check the motor for sludge build up. Third day, pulled valve cover and found black vasoline type sludge on head. They told Nissan warranty that I had never changed my oil, because I did not keep receipts for my oil and filter purchases. 8 months ago and 9,000 ago, they had to put a new valve cover on because I kept loosing my oil filler cap. Now, either it was not sludged up then, or they just covered it up. Sure sounds strange. So, my warranty was voided, and I am having to get my engine rebuilt on my own and document everything for court purposes. Nissan really stood behind me on this one, and you know what they were doing behind me don't you.