Not to much a tech issue but im half way through a complete rebuild of a type1 engine and the pistons could do with a bit of a clean and de cokeing , they havent covered many miles since they were new (4000) ish miles maybe so the cokeing isnt too bad but may aswell clean them before they go back in , whats best to use on them , i have used parrafin and "GUNK" on the case with good effects but not sure what to use on the pistons themselves , any suggestions, tips most welcome