I think this is probably the most important question in regards to the future of this great product. Some of the '06 bottles I bought last year were only a couple months old. Hopefully some '07 produced bottles will show up somewhere (perhaps Canada). With Castrol being a sponsor here, I'm surprised they don't have any "official" representation - it would be great if someone could give us a little insight.
I suppose there are three likely scenarios: 1) GC will continue to be produced and sold, but AZ won't be stocking it, 2) All stock of the product are being depleted and will be replaced with another similar formula (group III anyone?), or 3) They will no longer produce or import it to North America.
Short of any announcement from Castrol, we'll just have to wait and see how it plays out. Fortunately my stash should last at least 18 months so the verdict should be in by then...