Location: n.e. Illinois, July 2. (I didn't give the location originally so as not to prejudice responses since Rusty is uncommon here in summer.)
But I think you're right about juv. Starling. I can't believe I didn't even look at that page in my books or that I wouldn't have recognized the shape (although it was far away). In fact there were other birds with it that had a pale gray head and dark eye line, plus the reddish wings -- which would be consistent with Starling plumage "in between" young juvenile and molting juvenile as shown in Sibley (i.e., before acquiring the spots).
Thanks!