I know an older chemical engineer who worked on the lead issue for a number of years.
One of the official rationales for claiming that tetraethyl lead would protect valve seats was that the lead oxide layer left behind after combustion would form a perpetually renewed ablative coating.
This was accepted as an article of faith for decades, until when the great unleaded controversy started, SAE actually lab-tested identical engines, and learned that TEL in the fuel actually caused increased engine wear -- not just around the valves, but of all internal moving parts. Some of us remember when even meticulously maintained engines were uselessly played out by 100K miles.
I miss having really high octane for cheap, but the horrendously bad health effects of lead, plus increased engine wear, and its incompatibility with catalytic converters, made getting rid of it a Hobson's choice. It had to go.
What I find interesting is the speed with which the rest of the world is now ditching lead as well. Much of this is reportedly being driven not by health and environmental concerns, but due to automakers' cost structure. The manufacturers want to run production that is as globally uniform as possible. A case of their doing a collectively good thing for directly selfish reasons, which does happen now and again.
Now if we could only get rid of the ethanol and/or MTBE that the feds are perpetually forcing upon us and into our perfectly good gasoline. Sheesh. You would think the lead lesson would have been learned.