One thing I can add to this, the lead in the gas was done to prevent knocking, particularly in high comperssion engines. Any valve lubrication was strictly a side benefit. I will say that I did have hardened seats installed in my head, along with new valves, but that had more to do with the severly burnt valve on #5. Plus it was relatively cheap from the machine shop I use, $12, valve and seat, installed.
