I just bought a 2009 C70 but also own a 2001 Ford F150 with 145,000 miles on it. I have always used convention oil, not synthetic, in the truck. At 130,000 I sent a sample of my used oil to an independent lab to get tested. The results were "This truck looks more like it has 15,000 miles on it, not 130,000 miles. Whatever you are doing, keep doing it." I change oil every 4,000 miles and buy whatever is on sale, 5w-20. I am willing to listen to oil debates about what I should use in the C70 but I gotta say that I am really happy using conventional in my truck. But I also understand that the turbo has stricter requirements. My C70 manual says sythetic oil is not used unless towing. (How many C70's are used for towing?). OTOH, the manual says change it every 7,500 miles, which is a little longer than I'd like to go between changes. In my humble opinion, changing the oil often is more important than what type of oil a person uses. In the back of my mind I am thinking Castrol 5w-30 conventional, every 5,000 miles. Thoughts?