I ran conventional oil years back in my work trucks. It was run hard and hung out wet. Still, I sold my last truck with 188k on it to my brother inlaw who wanted to make a camper out of it. He ran it until it pretty much fell apart at 260k, everything but the motor. Ran as good as the day I bought it. Sure I could have ran a synthetic oil in it, but the only thing that would be different in the end was the cost of oil changes, by alot. There are more things on a car or truck that will cause more heart aches then the type of oil you use. A $40 timing belt can wreck your motor no matter who's oil you have in it. And really ,who would rebuild a trans in a car with 300k on it that's worth $1500 in good shape? When the people that do oil testing for a living say they use conventional oil in their vehicles, that should tell you all you'll ever need to know.