There are just too many variables and too many operational procedures that will determine engine life. I just retired an Irvine .36 that has accumulated around 170 hours of actual flight time. That would be the equivalent of 1000 10 minute flights. The primary problem with the engine is the rod bushings are worn out, and it needs bearings. Since the case, muffler and carb are still good, it will remain as a source of spare parts for the other three Irvine .36's in inventory. It's entire life was spent in the nose of a Andrews Trainermaster (an airplane like a Sportster), and that airplane still have a few more flights left in it. It was a kit that I started in 1985, finished in 1995, and is ready to wear out another set of servos and another new engine. Turns out that the servo motors chuck it in at around 150 hours.

I don't have much faith in online discussions of whether and engine is rich or lean. Only because most people that I actually see fly seem to be tone deaf. What they call rich is often pretty lean. They can have ball bearings growling under the engine and prop noise and be totally unaware.