I was around hundreds of pieces of small air cooled ope when I worked in parks. The only time any engine had a problem was when it got north of 15,000 hours (!) or it just ran out of oil because no one checked the level. The only pattern of small engine failure I saw was with tennis court blowers with various 8 hp engines. They consumed a lot of oil since they’d always run at 100%, but they still last 20 years.