Just spotted this thread, alot of guys will give you a long list off specific brands and certain things to use, I'd reccomend starting with degreaser then just getting in with small brushes and just alot of elbowgrease! Alot will frown at this but my secret ingredient was thinners which most will thing I'm crazy for using!But it works great!
Problem is once you start you can never stop Because the bits you haven't done stand out more and it gets to the point where the bits you just can't get to really p!££ you off!
I spent most off yesterday sanding bits off metal that were heavily corroded or oil stained which most people will never notice iv done, now that is sad but it looks good