I finaly got to taking my engine apart to re build it. Wen i took the pistons of one of the rings had some rust on it to the point that it was seced in place. I managed to free it, now my question is can i re use this ring if i use a light sand paper to get the rust of or do i have to buy new rings? And how would i know if this engine has been rebuild once before? Any help or tips would be apriciated.