You might want to try soldering the clip to the terminal to get a good connection. For old brass, you would want a strong acid-based paste flux. Just apply the flux, heat, and apply solder to the joint between clip and tab. I have "marinized" a lot of stuff this way.... Plumbers use acid flux, the usual electronic rosin flux probably isn't strong enough but is worth a try. Acid flux residue needs to be washed off before the item is used.
1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida