I shoot CO2-powered airguns a fair bit for amusement and vermin control, but some guns get through more gas than others. Unfortunately, if you leave a CO2 cartridge in the gun for more than a week or so you risk getting it stuck against the seal - my possum carbine may sit there for a month without seeing action in the winter. Lubricants like molylube and silicone grease just muck things up, so I tried PTFE threadseal tape:
It works really well. As an added precaution, change the cartridge when there is a small amount of gas remaining to blow the spent cartridge cleanly off the seal.
The tape goes just once neatly over the cap on the end of the cartridge, back down to the shoulder, then wraps around a couple of times to stop the tape coming off in the guts of your airgun. Don't put on too much tape if loading into a tight-fitting or corroded cartridge holder or you might wedge it in.