Dunno if that's overspray on the rear diff and gas tank. Be weird if it only got it there. Looks like a nice car: https://detroit.craigslist.org/wyn/cto/d/1972-buick-skylark-custom/6672188208.html
Looks like red oxide on the rear,and the lack of tailpipes blackened the tubes. Someone did that at some point in its life. Other than the door molding missing,it looks pretty good.
