air nailer bends nails

I have a Crafstman Framing Nailer (which must be made by Campbell Hausfeld because they look identical) which has started bending over nails. The ram also leaves an impression in the wood directly above the nail head. It does not have much use on it although it is about 4 years old. There is no apparant damage to the ram and I'm the original owner so it hasn't been abused. Could this be caused by one or more of the orings going bad with age? Anyone know a source of info to get help diagnosing the problem? I talked to sears and the person discreetly told me that based on the cost of repair estimates and parts, it was generally not worth fixing. But orings are cheap so if I can fix it I'd like to try.
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