I've been looking through 12 years of data on fleet vehicles of all types, sedans, pickups, mini-vans and suv's. Out of an annual total of 6 to 8 thousand vehicles, some with few records and many with every record, cars that were kept on an average of 3 years and 100k miles I found 12 drivers that have been there at least 10 years. There were 2 excellent drivers 6 good and 4 that were tough on vehicles. No matter what vehicle the 8 better drivers received the records of repair and maintenance were very good and the other 4 always had problems. It did not matter what vehicle the better drivers had, they had excellent luck and little if any unscheduled maintenance. Three of the good drivers drove mini-pickups and got over 100k miles on clutches and close to that on brakes. One of the bad drivers never exceeded 30k miles on a clutch in a mini-pickup, and about the same for the brakes. His mileage was much worse and he wore out tires and had many other non-scheduled maintenance problems. This look at the data is not controled or scientific but the picture I get is that the driver is far more important than the vehicle brand or the oil or anything else. We had a Mazda 323 with a 5-speed go 200k miles on the original clutch. It was a vehicle driven by a female that did not give it up in the normal rotation and so far, refuses a new vehicle replacement. This 323 is on 5k dyno oil changes and lives in good weather, and is garaged, every night and every day at work. It has never seen freezing weather or much rain. So in the end, I don't thing oil has that much to do with how long an engine lives. It's only a small part of it all.