Older Crosman 1377 Air Pistol. Believed to be bad seals. I'm told I can buys the seals from plumbing supply store and fix is easy to do myself with no experience. True?

if you dont have a cleaning rod for it you can go to your local bass pro/cabelas/outdoors store and get a cleaning rod for a .17 caliber for fairly cheap. you should be able to push the pellet out or clean it if there is dirt or grime in it. and make sure you use the right caliber pellet! (:

yes it safe to shoot bb,s in the 1377 pump pistol,i have 3 of them they actually shoot true'er and with more vilocity

Hi orichtero...
Take the air gun to the nearest roller bearing seller, they will have o rings also...they will be able to fit the right o ring for your gun for you
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Sounds like the O-ring inside the pump mechanism is bad or going bad. You can try to add a little lubricating oil and see if that can stop the O-ring from leaking.

Hope that helps!
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It's available in Adobe Reader format from http://www.crosman.com/pdf/manuals/crosman/1377/C1377-OM2.pdf

I just finished replacing mine it was easy. Use a small screwdriver in the slot and tap it in a circular motion until it loosen then it will come out easily. Go to the hardware store and buy a blue .5" maybe it's 17/32" X .125" thick. remove the old washer, the puncture pin, and the screen. Clean all of the parts with alcohol. Reassemble in reverse order and tighten the brass locking "screw" securely. It's a bit of work screwing it back in so be carefull not to round off either of the slots. I used a standard 1/4" and .125" screwdriver like it was a lever to spin it around. The smaller screwdriver at first the the lager one to get it tight. It may take pliers to tighten the new cartridge in mine did. Instead of doing it as I did and tighten the H__l out of it tighten and test in small incraments. Testing after each one. This does work and the seal are readily available in the plumbing section of good hardware stores. Happy Hunting

The pumps seal is bad so take it apart and cut a piece of leather out to fit
Coat the leather with Vaseline and it will operate just fine for you

Well that takes me back! I have an old Daisy 1200 -- essentially the same pistol in a different brand.

My Daisy has a hand-turn screw to hold the CO2 cartridge in place, and you have to tighten it quickly until the leaking stops. It does this by pressing the cartridge up against a nylon washer to form a seal (and of course pushing it into the piercing pin to get the CO2 out!)

With age, I'd expect that nylon washer to get stiff or crack, making it harder to form a good seal. You don't need an exact replacement part, but if that's happened to yours then you will need to replace it with something more-or-less the same size as the original.

IF IT SHOOTS HARD ENOUGH AT 8 PUMPS DON'T WORRY ABOUT IT.

the seal must be broken. send it back to whom you bought it from and get an exchange