thanks for the answers.i have this engine only two months.i was told that it was new.the sure thing is that the previous owner had this for 10 years sitting.maybe he run it one time and leave it inside the box with fuel.is it possible so much rust for two months?i did not use after run oil.maybe it was rust before me.the piston is very clean.i do not know.i worry , cause i have already ordered another one without breathe nipple(os 72a).