65 Dart Horn Problems

I've tried many things to remove that ring and like external snap ring pliers but they have to be of a heavy duty variety. anything wedged in the opening works. you don't have to open it up much for it to come off. Main thing is to not damage the horn contact ring which is easy to do. Others reading this may be able to offer better suggestions.
For insulating material I've used, plain old silicone, a thin leather disk, but prefer bathroom caulking. Main thing is whatever you use can't be electrically conductive. If using silicone you have to be careful to not squeeze it all out to the point the metal parts touch when reassembling. Let it dry thoroughly.