Sometimes we're contacted by folk whose QB78 family air rifle "leaks a bit" and they ask me what to do. The answer is that, before you tear the air rifle apart and install new seals or a new valve, try "The Pellgun Oil treatment".
Take a 12g CO2 Powerlet and add one good drop of Crosman Pellgun Oil to the flat tip, facing into the gun. You can use a pre-used Powerlet as the second one, facing out towards the front of the gun. Tighten the Tube Cap as usual and "dry fire" the gun with no pellets until the CO2 from that one Powerlet is exhausted. Then stand your gun in a corner and leave it for 24 hours. Load new Powerlets and test fire.
Miraculously, the leak will often have disappeared!
So what happened? Well, the Pellgun Oil has been blown through the gun and coated all of the seals and O rings. The oil causes dry O rings and seals to swell just a little and this can often "re-seal" your gun and eliminate the leak.
If this doesn't work, don't despair, just repeat the treatment. Sometimes I've found that a couple of attempts are necessary for success.
Archer Airguns sells Pellgun Oil on our Accessories page at http://www.archerairguns.com/Pellgunoil-p/pellgunoil.htm.
But if this fails, then you will probably need either one of our Seal or Valve Kits - together with maybe a copy of my 88-page "QB78 Family Workshop Manual". Plan to spend some "quality time" bringing your QB78 back to health. But at least you tried the easy way first...
Oh yes, this trick also works for the Crosman 160, 167, 180 and similar CO2 air rifles. If you have one of these old guns and it's not been fired for years, the "Pellgun Oil treatment" could be all that's required to have it shooting again like new!