If I blow this picture up a little bit, the receptacle looks discolored but not too much right near the screw(s), more so on the face of the receptacle. Might just be 30 years of grime.

Pauluk - my guess on the grounds up on the receptacle on the right is maybe the molded plug for the window AC cord is made with the ground up when it hangs down. Maybe? I've seen similar ones but I don't know why they make 'em that way.

Radar

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