Pff Coasties are no fun!
Not sure but it sounds like an internal leak, since the system is so new I don't see why they wouldn't just redo the seals. Unless one of the sealing surfaces is messed up, like the shaft.
Marine hydraulic steering systems are usualy pretty trouble free, I never really had to deal with any problems with them. Sorry I can't be of much more help to you.
Post your diesel problems in the diesel forum, you might be surprised and get the info you need.