Update.
Actually I haven't moved on that much.
I did buy a set of tools and chemicals from Autopia: PC 7424XP, backing plate, pads, clay, M105/M205, and associated cleaning agents.
Figuring out what to get was difficult for me as there a lot of products and biases out there.
I did try it on the area that wasn't oxidized much immediately around the sunroof (I am rebuilding that mechanism and didn't want the new seals affected by the buffing) and it turned out to be like new.
But GorillaFoot's recommendation to go to
www.Autopia-carcare.com's forums was the right ticket. Extensive knowlege-base, lots of helpful people and wiki's there, just like here!
I'm working on other car issues now so it'll be a couple weeks for pics.