Is there some sort of protective coating on the Defcon III Skylons that traps water spots? I can't get them clean. I've tried metal/aluminum polish and shower/tub cleaner designed to attack hard water buildup but the spots won't go away.

I just buffed out my Defcon 4's with Mothers Polish from Advance Auto Parts. They were pretty bad and it took a while. I really had to scrub them to get them polished out. They look great now. I keep them covered with sacks now to avoid having to go through that ordeal again.