No lead....less in fact as it would have worn away, and still the problems went away with timing changes.
That's dealt with in a couple of the papers. I think the Barlow one is best from memory. From memory its about changing the temperature profile of the valve and it also derates the power of the engine.
Mogas also has other additives to replace the lubricating properties of lead to some degree. It is not without lubricating properties entirely. I haven't paid a lot of attention to it, but I think Potassium is one and MTBE may be another - although it is controversial, and I suspect that the industry may have moved to something new. I forget what was behind Shell's move from Optimax to V-Power, but involved a wholesale change to the fuel's chemistry.