Are they rebuilt with new O-rings yet?
Take the in/out posts off, and pop the spring loaded poppets out, soak them in hot water with Oxy. Take the dip tubes out, soak the short one with the posts but put the long one inside the keg and soak it in there.
To clean the outside, use a 3m scrubby pad or the back of a sponge with some Oxy or better yet, barkeepeers friend. Use a razor blade to scrape any stickers or residue off.