Marvel mystery oil used as a lead substitute?

The lead substitutes that are effective, legal, and somewhat available contain a chemical compound abbreviated as MMT. The middle "M" stands for manganese. Sort of like ZDDP in motor oil, it forms a sacrificial barrier on the valve and seat that prevents them from welding to each other and degrading the seat.

Amsoil's octane booster has this MMT. I use a bottle every other half-tank with 90 octane E-0.
Other brands have MMT, but not all.

I'm not going to discuss whether or not it's necessary. Do what makes you comfortable.