About the leak, I seen happen on one of my friend's rifle, on the regulator adjusting screw, there is an o'ring there that wasn't sited properly, took it out and resited.
On another one, was on the dynamic wheel brass tube, also an o'ring between the tube and the breech was squashed took it out and replace sited properly.
Another one is on the right hand side of the breech, under the pellet guide, there is a small brass screw and 2 small o'rings, they were damaged replaced.
On my case, was on the top valve (above the gauge, an o'ring gave up, unfortunately, could replace it myself, as is temper proof and I had to send it back to Huben to fix it.
These are the ones that I have seen, give more info and I am sure Gregor that have more experience with the rifle can point you in the right direction.