i've used castrol super clean and had decent results getting parts clean, but once that white plastic gets that yellowish stain to it, its pretty much impossible to get WHITE again. i've tried bleach, softscrub, boiling them in bleach... nothing worked.
i did ask a guy awhile back who had some really white used associated parts on ebay how he got them so clean, and i forget the name of the brand but he used some kinda drain cleaner... i havent yet tried that and i doubt it would work anyway.