Ok airseal trouble shooting 101 guide
1. Disassemble so you have it in these 3 pieces
A) stock
B) trigger/receiver/cylinder set (all still together)
C) outer barrel/hop/inner barrel (all still together)
2. Grab part b above, rack the bolt, cover end of cylinder head with thumb firmly and pull trigger.
You should be able to hold your thumb here for 10 seconds plus and the piston should stay partly back compressing the air. When you let go you should hear a thud and air rush out as the piston hits the cylinder head.
When you pull the trigger listen out for any airleaks from the piston head. Or from the trigger area as these tell.you if the cylinder head o-ring needs replacing or the piston o-ring. If these aren't leaking go to next step.
3. Assemble parts b and c, rack bolt again cover end of inner barrel firmly with thumb (may need to remove muzzle cap to do this) and pull trigger. Again we are hoping the piston doesn't hit the cylinder head and when he let go it does. If air is leaking at this stage it's likely to be between the cylinder head to hop rubber. (Could also be hop rubber to barrel seal but that's not the main culprit in stock rifles.most of the time).
Try these 3 steps and report back.