...the screw is Good Idea.
Just want to add, the Rubber 'Cap' you have on the Heater hose barb, is perfect to Finish-Off the Stud that remains after removing the Wiper Arms. It Snaps on! Looks Nice. I put one on each.
MJ
P.S....I would have taken a Center-Punch and a Heavy Ball-Peen Hammer, Hit near the rim, of what looks like a Freeze Plug, clearing the edge of the Counter-Bore, to 'Cave-In' the Thin Metal. The Opposite edge will pop up, then grab with a Pair of Channel-Lock Pliers and work it free. Not enough room the Swing the Hammer? There is Always a Way!