When you don't drive them seals dry out and become brittle, then leak. The AC compressor looses it's charge, valve springs begin to loose tension on valves that are open etc etc
While the GT is a very nice car I doubt that the increase in value from having a very low mileage example will be enough to compensate for not having use of the car for years. There are still well over 3000 of them out there so not that difficult to buy one. I run the crap out of mine and enjoy every minute of it.
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