I just sold a perfect FWB 601 without scratch or blemish. I shot it recently and it behaved flawlessly. I removed the stock from the rifle and "overpacked" the carton. When it arrived the buyer assembled the rifle, cocked it, but when he closed the cocking arm the air hissed out. Long story short..... a near perfect rifle suddenly will not hold air. I do not know when the rifle was last serviced, but as I said it was functioning flawlessly . Is it possible that something came loose in packing or shipping? Thoughts, ideas?