The seat is what suffered at the loss of leaded gas, not the guide. But the loss of lead in gas wasn't normally a problem for most industrial type engines as they had hardened valve sets already. Not just Ford, but Deere, Continental, Perkins, etc. etc. Many even had valve rotators that turned the valve a partial revolution each time it opened, keeping the seats free of carbon. This more likely to be seen in OHV engines.
This aside, Marvel is still a great fuel additive IMO. I started using it in older Harleys that didn't yet have hardened seats, at the urge of an older fellow I once bought a motor cycle from. He told me to just use a cap or 2 full per tank & not to use it every tankful, just every other one. Said it was so good, that it built up in the system & if used too often, the engine would begin to puff smoke. He said you can plainly see when you've used it too often. I thought, BS! It was not BS.
I don't need it to lube seats in anything I now own but have found another use for it. I winterize fuel systems with Marvel. Way better results for me than Stabil.
