I pulled the head on my Bobcat loader last year after 25 years of hard running. I can't remember exactly how many years we haven't been able to buy leaded gas, but it has to be around 15. I expected to see the valves pounded half way through the cylinder head, and instead I found a small piece of carbon had lodged between the seat and the valve and the head and valve were in perfect condition.
I have always used a gas additive that does not state that it compensates for non leaded gas, and always thought it would just prevent valve guide wear. I can't say whether or not this additive was the reason that the seats looked this good, but I can say that this engine has worked very hard on no lead gas, has soft seats, and no harm was done.
I have been running a F#$^ big block for the last 8 years with soft valve seats on no lead gas. I have taken many long ( up to 2000 miles / trip ) holidays with this car, and the engine is still running great.
Bottom line, I worry about the problem, but it hasn't happened to me.
Bob
