My Crosman 1377, circa 1994, would not pump any more so I threw some silicone oil at the pump cup area with a syringe.
I have to stroke it fast to get a good stiff pump. She would still not pump if I pumped really slow. I still get an occasional loose pump if I pumped real slow. I get good fps if I shoot right away, but if I let her sit for a while I lose pressure and fps.
Your sage wisdom will be appreciated.
Ponz
There are three kind of leaks to the old pumpers. The most common is a stiff, hard, pump plunger, that will leak past the plunger while your pumping.
The other two are in the valve.
A check valve leak, will be leaking toward the plunger, into the pump tube.
With the gun cocked, a popit valve, will leak into the chamber, or into the barrel if you close the bolt.
Sometimes the hammer can hold the popit valve open, so I've just got in the habit of always cocking a pumper before pumping.
If you listen close somtimes you can hear, and identify the leaking valve.
I have had some success just cleaning them, by pumping all purpse cleaner through them. My theory is that oil eventually finds its way into the valves bringing dirt with it. The dirt gets lodged between either of the two valves and the valve seat, causing the leak. Flushing the valve with a cleaner can remove the oil and dirt.
If the pump plunger is hard it'll need to be replaced.
If you get it clean and charged, put a full load in it and see if it is still holding it the next day. After that always store it with a charge, to keep the valves seated.
There is a fourth possible leak, but it would be the O ring on the bolt. That one would only cause blow by when you fire it.
