...but no power. If it was pumped up, it should have had some power.
Elsewise there are leaks. If you are considering tearing it down, consider this:
Squirt plenty of oil into the pump tube. Get it in there any way you can. Pump it several quick strokes and see if you gain good pressure that will hold. Sometimes that is all it takes to get the seals and valves functioning the way they had ought to.
The excess oil will eventually be shot out if that corrects the problem. If not,you can always tear down the gun.