Ok, I took my top-end apart for powervalve service and found some minor scoring on the intake side of the piston (enough to catch a fingernail). So I've decided its time to replace the piston as well. My question is do the KDX's come with various size pistons (like A,B,C)? The one that came off of it had an 'A' on it. And if so how much difference in size is there? Are you safe in going up a size? Thanks.