Wife just purchased a 2002 Buick Century. While reading through the manual I found that GM recommends changing the oil within two tanks of fuel from when the "change oil" light comes on. No regular or severe service mileage intervals listed at all. I haven't talked to the dealer service dept about this yet but think I will have the oil changed at 3000 and 6000 miles and then change to synthetic and go 5000 between changes. I read somewhere that all 2002 GM vehicles are the same. Any comments?