We've been gone for 3 1/2 months with the Bonneville sitting in the garage the entire time. The good news was that after I reconnected the battery, it started right up and ran perfectly. The bad news was that I noticed a very thick lime green fluid on the garage floor under the engine, towards the front and to the passenger side. I still run Dexcool so that isn't it and for the life of me, I can't think what this might be. For what it'* worth, there is no smell to it at all.
Any ideas?

Now that there is more light in the garage and I have my old clothes on, I poked around some more. It appears that the AC compressor has a coat of this stuff on it so best guess would be that the oil and presumably the refrigerant have both leaked out.

The verdict is in and it is in fact the compressor that died. Since not fixing isn't much of an option, I asked the repair shop if they had a recommendation on new versus rebuilt. In their opinion, new was the way to go(at $400 plus installation).
Does anyone have the part number so I can check GMPartsDirect?

Thanks for the information. GMPartsDirect shows a list of $600 and their price of $312 but with *&H it came to $380. I'm going to ask the mechanic if the price he gave me was for a GM compressor or for Brand X.