I just purchased a 2006 Range Rover for the wife and was reading the owners manual, yup some of us still do that! I noticed that the oil sump holds 8 quarts of oil which is nice, but Land Rover specifies Castrol GTX 5-30 with the first change at 7,500 miles. I spoke to the head wrench at the dealer and he felt this was very reasonable considering the large sump. Should I really do my first chage at 7500 and would everyone continue to use the recommended GTX 5-30 until the warranty expiers at 50,000 miles? I am leasing this vehicle and should give it back at 48,000 miles but if I like it I may consider purchasing it. I live in NY so it will see cold temps (maybe 0 degrees) and heat to about 95 degrees. The car will be used 50/50 higway and street use but since I live in a rural area it will get at least 5 miles even on the shortest run. BTW the vehicle uses a cartridge filter which it seems nobdy carries except the dealer Any thoughts?