The valve thing is urban legend, insofar as there's no evidence that TEL mitigating valve seat damage was a known phenomena before the 1960s. So mitigating val

The valve thing is urban legend, insofar as there's no evidence that TEL mitigating valve seat damage was a known phenomena before the 1960s. So mitigating valve seat recession was not the motivation of TEL when TEL was adopted and only became a motivation for keeping TEL decades later when the effect was discovered.