My friend's dad never had a car problem in his life. His theory was simple -- don't introduce a clean liquid to a dirty system. Based on this premise, he never changed his oil or any other fluid (besides gasoline) in any of the cars he owned. He'd check his oil and top it off as needed, but he never bothered to change the oil or get new transmission fluid. Then again, he always bought new cars and traded them in when they hit 60,000 miles. I'd like to meet some of the folks who ended up buying his old cars to see how long they stayed in one piece.