Well way back when  

 I used to fly these similar engines on a cert planes. We never ran them lean of peak gami or not

 Actually gami wasn’t around then I don’t believe and the fuel was 4 grades  ranging from 80 through 145  oct   g-a-r-b   [ green amber red blue ] do you remember those colors well the lead helped lub the engine as well .I think the heat is destroying these engines through several issues

 Lean of peak, poor induction air cooling and no lead  additive   I really think the best way to tell if you are going to far into lean of peak is look at all the blue parts that are in the engine at break down  . Everyone seems to want the lean of peak and I don’t understand that other than the fuel cost. I guess do what you think is best fuel cost or engine brake down at half tbo  the real question is are you making the tbo and  I have heard of only a few that can say they are   These engines were certified  back when fuel was leaded and the numbers represent cert not 100ll

 My best guess on total times is 2500 hrs in c 206/ c 210  and 7500 hrs in other cessna 150 through 421  all this time was in the late 60’s and 70’s

 My thoughts are only mine so when you brake down at less than 500 hr maybe you are running to lean also maybe we should get a chart of actually who is running lean of peak with gami and cert and the actual hrs it ran before brake down on the whole fleet Bill  Maddox