Hello; I don't know about OS, but I have an old Saito 45 that has had more then 66 gallons of fuel though it. I started counting in 1991, after I put new bearings and a new piston in it. My own longest living OS engine is an old 90, the type with the pushrods going up the back. That one has run (for me) since 93. I think that as long as you can get parts for it, theres no reason why it shouldn't last forever.