Leaks CAN be caused from a dry gun, so after you get a full tank, if the problem is still there, try putting 5 drops of oil in the ASA and cycling it 20 times or so to work the oil through the gun. If the problem is still occurring, then you can look into a new cup seal.
Another problem people seem to have every now and then is a leak at the RAMAIR chamber. But this leak should be easily identifiable as coming out the tip of it, so this is probably not the case. (If it is, you probably need to oil the piston O-ring inside)
I've had the same cup seal for over a year and it still works fine, so try the above options first.