He said he used oil and those rust spots are whats left. 6000 grit is very fine and wont scratch, just work the surface where the rust is. Why replace the o-rings? He didnt say he was flaming out or going from rich to lean. He is mud bogging. The silicon at the bottom of the heatsink and at the back plate is to give it an additional seal,preventing water from seaping in and any air from escaping....I think I have seen a pro or two or a THOUSAND do this What do o-rings have to do with anything? He didnt say he had carb problems