I have seen ancient CO2 guns working well (usually Crosman and Daisy), but I have seen many many relatively new ones leaking like a sieve.
As said above quality counts, but physics being what it is eventually the seals will fail and some of these modern blowback semi auto things are just waiting to fail IMO.
You can confidently buy a pre-war spring air pistol, I wouldn't be confident buying a second hand CO2 gun of any age unless it said "2240" on the side of it.
Treat them as disposable - not least because the market for these guns is so fast moving that the chances of buying replacement parts a few years later are going to be slim.