Marvel mystery oil used as a lead substitute?

I just did the googling and I haven't seen any website that says yes. I would be very leery adding any unknown stuff to an engine. Seafoam yep, states right on the bottle. My X heads don't have hardened valve seats, machinist said you'll never drive the car enuf to warrant them.
Exactly.....but the fact is, you CAN drive the car as much as you want. What dictates hardened seats is exhaust temperature. Your car is so light, the exhaust will never be hot enough to warrant hardened seats. But you cannot tell people that no matter how much you preach it. Our light cars with good cooling systems and decent gears just don't generate enough exhaust heat to worry about.