Just been messing about with the Dragon over the last few days at home - the main problem with assembly is that the long legs seem to warp during the casting process - demoulding, when the resin is still soft, means that the ankles flex - the left leg suffers from a slight rotation of the rock, and both legs seem to have minutely straightened out a little, which pushes the main body away from the tree trunk, causing the gaps Richard mentioned. it's rather unavoidable.
To easily fix it, you need a hairdryer with one of those diffuser/focusing nozzle attachments (I'm using a hairdryer that cost £5 from Asda) so that you can apply heat to a specific area without burning your fingers.
Best thing to do, is to glue the legs to the torso, then gently (well, not that gently) force them into the correct position on the rock, using your Crushing Grip action to get the left rock to slightly rotate and lie flat in place. (The Dragon's left, not your left) Once this is in place, use a hairdryer to heat the ankle enough that it becomes more bendy, you'll be able to tell as it will stop resisting your Crushing Grip. Remove the hot air and let it cool whilst still holding it. It will now be 'set' in the correct position. Glue it in place.
Now attach the tree trunk and the left arm (prepare pins for the finger to hand connection first) - you'll find that if you apply pressure to the back of the dragon, you can easily close the gap between the hand and the finger on the tree trunk. Again apply hot air to the legs whilst gently pushing the dragon into place as above.
This should solve any huge gap issues anybody has had. The extent of the problem will vary from casting to casting.
Currently altering the rock and tree trunk so that there is less need to mess about with hairdryers, but that will only apply to future Dragons, obviously, as it means new moulds etc and thus will only kick in when the current ones are replaced.
(Messing about with the Dragon after a year off makes me want to start again for the most part, using polymer clays instead of greenstuff, procreate, etc. I would do it differently now, that's for sure.)
(I am not starting it again, just to be clear)