..a blown valve stem seal. Crosman is a simple system, and the most likely casue of the leak you describe is from that valve stem seal.
Not uncommon, the parts are cheap, and you can fix it yourself. Perrsonally, if possibe, I'll keep at least one spare entire valve assembly on hand ($15? $17?)...when I have a problem, will swap out the whole valve and fix the troubled one later on.
but if you can exchange it, then go right ahead...that's the easiset way to fix it.
Will try to hunt up at least a parts list for you.
Here you go. the part i suspect is leaking is marked 2250-016. Crosman responds to phone calls, but you may as well order a few more things to get some value from their shipping/packing charge.