Hey Bob, here is another detail to support your statement:

Valve recession occurs in older heads with soft, cast iron seats. The solution to stop the recession is to replace the seat with a material that is harder....typically Rockwell 45 or so. Lets see.....
the lead is a cushion to a soft seat and all we do is to make a seat hard and remove the cushion.....kinda backwards logic if the lead is a cushion since the harder seat would need more cushion.

The lead info is kinda like the sugar in the gas tank legend......it won't hurt your engine but folks will argue forever that it's true.

Here is some info from the net:
"A small amount of valve recession results from normal high mileage wear, but it can also occur when unleaded gasoline or a "dry" fuel such as propane or natural gas is used in an engine that isn’t equipped with hard seats. Recession takes place when the seats get hot and microscopic welds form between the valve face and seat. Every time the valve opens, tiny chunks of metal are torn away and blown out the exhaust. Over time, the seat is gradually eaten away and the valve slowly sinks deeper and deeper into the head. Eventually the lash in the valvetrain closes up and prevents the valve from seating. This causes the valve to overheat and burn. Compression is lost and the engine is diagnosed as having a "bad valve." The seat also has to be replaced, but it many instances it may not be recognized as the underlying cause of the valve failure."

The above suports Bob's statement about "tiny bubbles" being transferred......it's almost time for tiny bubbles anyway.