6.5mm x 1.5mm Co2 Tip Rubber O-ring Seal

[hallwoo]

Most leaks slow or fast can be repaired  by just sticking a tiny rubber O-ring on tip of co2 cartridge using silicon grease  or brake lube

then screw the co2 bulb slowly in  until it's pinched by the valve needle  , keeping   it straight in while holding the co2 cartridge, try not to make it rotate while screwing it in

this will save time in disassembly and possibly losing vital parts like springs and sear pins

this should work even on a co2 airgun with hardend and crumbling seal, no need   to remove it, just screw-in a new rubber O-ring   

I use the Harbor Freight 125 piece kit item # 67605   

if gun still won't hold the gas charge over a day, then U have additional internal leaks  like tiny O-rings on the nozzle  port or tube connecting to  co2 port
valve body parts