Acid water etching rarely ever has a happy ending. I've had some success with clay bar (mild case), buffing compound (moderate case) and sanding and polishing (extreme case). If it has gone all the way through the clear you don't have very many options. Try applying a glaze, if the appearance of the spot goes away then you can polish and wax, although that is temporary - the next wash and you have to do it all over again. If you run water over the surface and the spot disappears then a new coat of clear will solve the problem. If the spot still shows through the water, the etch has gone down to the color coat and a total repaint will be needed. That, or you could learn to live with it. Yeah, like that's going to happen! Since it sounds as though you've already tried an aggressive buffing I'm afraid you're looking at a more extreme solution. GM offers acid rain warranty, any possibility of relief in that form?
