A very common occurrence with CO2 Airguns and Airsoft guns are leaky CO2 seals. Usually this occurs right where the CO2 cartridge connects to the main valve area. This can be either in the gun or in the magazine depending on the setup of the airgun.
There are many reasons why this can happen, but the most common reasons are a worn-out or dried up seals or even a seal that has been imprinted or misshapen from the constant pressure of the tip of the CO2 pressing against it.
When this happens you may encounter a leaking CO2, the severity of the leak can vary from mild slow leaks to leaks that can be so bad that the gun is unusable. Keep in mind there can be other problems not related to the CO2 seal such as in the valve area, the fix I show you in this YouTube video will not fix a leaking valve, you can try using something like Crosman Pellgun oil for a problem like that.
Watch my below YouTube video where I show you how you can easily use some Plumbers Teflon Tape to improve the contact points between your CO2 and CO2 main seal and eliminate leaking CO2 in your Airgun.