Originally Posted by fulnix
I highly doubt it. No air/dirt generally passes over the valve O-rings. Usually the only way these go bad is if you have used a caustic lubrication like WD-40. My fist bet is on it wasn't cocked or has too low of an input pressure. I've teched a ton of guns and have only seen valve O-rings be bad when you install the valve incorrectly and nic one on the way in. Other than that they usually don't go bad.
Age also eventually claims these rings, suboptimal lubrication is pretty common with markers that have some age on them, either through disuse/drying out or the use of older, less advanced lubrication (or bad lubricants entirely). I have seen many bad valve o-rings and actually I can't recall ever encountering a bad valve stem personally.
Remember the Trilogy is going on 8 years old now.
Come to think of it, the valve retaining screw could be loose too.