100mm f4.5 Tele-Lithagon for Argus C4 (No4)

item #100mmf45lithagonArgusC4No4. The front glass has a 4mm ring around the edge at the back of the front lens element. It looks like this would clean off. I think it is oil from the lens that got on the underside of the front element. Condition 7-. With original hood.