have an air gun that is older than 25 years, but it used to work just fine until recently, when it lost so much power that it wouldn't even shoot the pellet out of the barrel. Upon disassembling it, the piston turn out as can be seen in the image. Can someone help me on what type of piston seal does it have, or if it even has one? and what type of seal I should place on it. I know its extremely old, but its the gun I grew up with and I want to keep using it.