I'm not Jerry, and I certainly don't have his knowledge or experience but virtually no cars need hardened seats except maybe high revving race engines that get beat on constantly.
When the US mandated the removal of lead from fuel, every car on the road didn't suddenly burn its exhaust valves nor did they die premature deaths. Contrary to popular belief, unleaded fuel wasn't introduced in the 1970s. AMOCO introduced its famous super unleaded in 1923.
Every vehicle I own and drive uses unleaded fuel with no additives. None of them have hardened valve seats. I've put 150,000+ miles on my '56 Cadillac in the last 20+ years and it burns unleaded fuel without any problems. Ditto for all my other vehicles from the pre unleaded mandate era.
