That is a pretty simple repair that you can do yourself. I just repaired a Slavia break action. It's usually the seal at the end of the piston that needs to be replaced or the "O" ring at the breach (or both). I ordered the parts from fleabay and they came from Australia in two weeks for under $40
Try sending Travis at AGS an email. Maybe he can help you out.
To make it simpler what model and brand of airgun is it? Parts are so much easier to find.




























