I could see springs, but most new vehicles have hardened valve seats that don't need tretraethyl lead for lubrication. Ferrous metals, when used in a correctly

I could see springs, but most new vehicles have hardened valve seats that don't need tretraethyl lead for lubrication. Ferrous metals, when used in a correctly designed part, have a near infinite fatigue life. https://en.m.wikipedia.org/wiki/Fatigue_limit https://en.m.wikipedia.org/wiki/Fatigue_limit