Andrew, I have a 580B and correct manuals, and in searching out parts there seem to be a few things that MAY be different between B and C models -
Equipment Parts Source ( Equipment Parts Source, Aftermarket, Case, Backhoe, Crawler, Loader, Dozer, Tractor Home Page ) has been a good source for cylinder repair kits, but you MUST know which cylinders your particular machine uses, which requires teardown of at least ONE of them BEFORE you order (Don't ask how I know) - Case used at least two different diameter cylinders on the hoe boom on the B's, plus one piece or split pistons, etc - same with some starter parts and probably others.
John's link (thanks, John) looks like a good resource, now bookmarked :=)