Believe that my benjamin 392 air rifle, which doesnt hold any pressure when pumped, has maybe a totally useless pump seal, which looks good enough but still no pressure even when coated with grease,, OR the valve is rapidly leaking back the air into the pump cylinder as no air is leaking into the pellet barrel
Answers & Comments
Apparently the o-rings rot. This company has repair kits available
http://www.pyramydair.com/a/Accessories/Parts/73