After the rings rust, then the rust builds up between the cylinder walls and the pistons and wedges everything tight. Rust expands - Iron oxide takes up 10X the space as iron, it can break things like freezing ice. I recently heard of Fluid Film - sold mostly at John Deere dealers, said to be even better than Kroil. I'm going to try some. Also heard #1 oil is fantastic - It's like #2 diesel oil but thinner. So thin it's hard to keep it from leaking out of pipe fittings. Don't know where to get it though. Sounds like thin viscosity is important, like the ATF/Acetone brew. I know it sure can be hard to keep ATF from leaking out of gaskets and o-rings sometimes.