The engine is about 8 years old but has only been run for the last 2 years, about one or two gallons of fuel, mainly sport flying. I have hit the ground several times, flying in a large pasture while our flying field is being rebuilt as part of a new ampitheatrel. The piston is clean and not visibly discolored, and I am careful to not run my engines too lean. One scratch is visible clearly and can be felt with a fingernail. the bubbles seen on compression tell me that loss of compression is serious. Gentle pressure maintained on the prop will all the prop to gradually turn as pressure is lost. I have 3 other OS engines and all have more compression than this one. Odd thing is that it just quit after 4 excellent flights the day before.