I to have never understood this debate about the use of unleaded and valve seat recession.
1/ Lead has always been added only because it was a cheap way of counteracting pre-ignition when engine compressions went up
2/ I very much doubt the theory of lead forming a protective layer on the valves and seats. If I remember well from my school days, the melting point of lead is about 300 and some degrees Celsius. The temperature around the exhaust valves can be 3 times as high, so any lead should be burnt away immediately
4/ A couple of years ago I had to take off the head from my Morris because of a blown head gasket, and as it's a 6 cylinder 2.6 engine and you don't want to take the head off to many times because it's so heavy, I also replaced the exhaust valves. I found them heavy pitted, in spite of running on leaded fuel all of there life.
It seems to me that a lot of people are abusing the abolishing of lead in petrol to sell there products, whether it's something to add to your fuel, or to earn some money in converting engines.