Sorry if this has been asked a hundred times before. I've searched and searched and searched some more, but all I get are mentions of the GC, but no specific comments on where to find it. 1 - Where can you buy GC? (I live Houston, Texas) 2 - What viscocities does it offer? 3 - Is it a Group IV synthetic? 4 - Any comments on GC vs. "the other guys"??? The Castrol website was useless. But I know you guys will have the answer!