Just how bad is it to run unleaded fuel in a car WITHOUT hardened valve seats ? I've read that at the peak of leaded fuel the was 3% lead. And by the end of leaded fuel it was .1% lead. Also read that you would have to drive like 70mph 24hrs for a heck of a long time before harming a engine that did not have hardened valve seats. If its a huge deal , I'll update. but for a daily 5,000 mile a year ride, is it all that important ??