Give up trying to stop valve recession with unleaded fuel. It cannot be done, the 'lead' additive you can buy really does nothing. True lead additive is so poisonous it cannot be sold over the counter. You CAN get the zinc, but you'll know that too by the extra cost, to be able to market it the oil makers had to agree to pay a fee to EPA, why that oil is so expensive and specifically marked as for 'off highway use ONLY'. People used diesel oil for a while, now EPA is forcing that zinc content out too. Mainly because the carrier is zincdithiophos phate, the phosphate is what EPA wants off the highway.
At this time, one of the best zinc oils is Valvoline for motorcycle, EPA not worried about bikes yet, not enough of them. But again, you will pay through the nose for the oil.
Even the newest engines show some small amount of recession, my Zetec Focus cars show it at 100K miles. Pull head and freshen up exhaust seats and the quickest 10% HP increase you ever saw. No need to touch the intakes.