I couldn't see, but he was getting readings. The Compressor had dye on the casing joint, but again, I couldn't see where it was coming from. He connected to add 12oz. of Refrigerant, which got it working. It is still working a week later.
I wouldn't recommend replacing the compressor just yet. If it loses some of its charge every 11-12 years, I wouldn't be too concerned about it. To properly maintain a GT, it should be started occasionally and each time the car is started, the AC system should be exercised.
Ditto what nota4re said: I've gone for years with compressors that leaked a little on other cars. Usually a charge for the season will cover it. I had a GMC van that I added two cans of refrigerant per year, did that for 8 years and it never got worse. You can add refrigerant yourself with some simple tools. In fact most auto parts stores now sell cans with gauges and connections already on them. Not the best, but good enough.
To quote my old nuclear engineering professor, "everything leaks," the question is, how much? If you car has never had a recharge, holding it 12 years is pretty damn good! At any rate, if you recharge it, and it doesn't lose most of its refrigerant for several more years, you know it's good. If it loses its charge in 3 months, then consider changing the compressor. But as others have noted, use it more often, and the seals may work better and hold the charge longer.