Older engines really do need the lead. A friend of mine is a Hemi-addict (he has like 15 of them), and he said that up until somewhere in the 40's, all valve train components were hardened. Then, the bean counters (no offense intended) learned that since the lead acted as a lubricant, they could save a few bucks by not using the hardened components. It was that way, up until whenever they started using hardened components again. I knew it was sometime in the 70's, I just didn't know when. So if you run unleaded gas in an engine that was meant to use leaded gas, it will eventually fail.