I have a 2003 S/C. I waited until the first scheduled maintenance (3,750 miles), then changed out the oil with Mobil-1 Synth 5W-30. I currently have 11K miles on my Xterra and still drive gently. I do kick in the S/C from time to time to let her stretch. Per the manual, I avoided hard acceleration/high rpms until about 1,200 miles. It was not easy. I have owned 5 Nissans in the past and find the engines to be very well built. When something went wrong, it was always from another part of the vehicle.

-dp