I have a Sheridan pellet rifle that uses Co2 cartridges. ( It's about 25 years old) . It still fires if I put in a new cartridge, but if I wait a day, the gun loses pressure. Has anyone replaced seals on a CO2 gun? Do I need to get special o rings or seals? Are there any tricks to install the seals? I'm thinking of going to an auto parts store to get o rings. I tried to find a set of O rings specifically for the gun, but I struck out. Sorry this is all one paragraph, can't get the return key to work Thanks, Bill