Hi Geezer
The bad news is that I class the Dragon as an overly complex gun, in that the stripping and rebuilding of them is a bit complicated, to say the least.
The good news is that all the seals which could give rise to your leak are simple common or garden O rings.
I believe the BBS expert on these guns is member JustinThyme :-
http://www.airgunbbs.com/member.php?118393-JustinThyme
All the best Mick