I had a 2240 that started leaking.
It was the seal that goes where the nose of the cart fits against the valve.
I was going to try an oring, while I ordered the correct part & waited for it to arrive, but I found a complete spare valve assembly in my parts box, so I swapped out the seal and its been working fine ever since.
Try warming up your rig with a hairdryer. Focus the warm air on the area where the valve sits, outside the frame & tube, thru the loading port, and down the CO2 tube, then while it's good and warm try piercing a cart.
Sent you a pm.....