FWIW, I bought my O-200 with 1700 hours. I went on the newly created "On condition" program, and ultimately ran it to 3550 hours (with 4 overhauled cylinders along the way). I took it apart because of ferrous metal in the filter. It turned out to be only shavings from the alternator drive coupling cover - the engine was fine inside, it would have gone a lot longer. A well cared for engine, with regular oil changes, will go for a very long time, and as BPF says, they very rarely just stop, they nearly always give you lots of warning - if you're doing the maintenance, and paying attention to what you're seeing...