Depends on how you define "best". Best cleaning would be Castrol Super Clean, however it will still be oxidized. To remove oxidation you'll have to polish it and coat it with something. That type of metal just oxidizes naturally.
oxidation wont hurt it. now are you talking about gunk build up. cause i just cleaned mine. And i used carb/tb cleaner. sprayed it in there and used a air hose. you can use a rag to get the chicker parts off.