When I replaced mine, I took a part the door and I worked from the inside to remove the ferrules so I wouldn't harm the outside of the door. I finally collapsed them with some pliers and Vise Grips so they fell out the front or out of the door. The metal is pretty soft, so it's not hard to collapse them.
When I put new ferrules in, I bought two new rubber "O" rings just the right size to fit over the new ferrule behind the flange of the ferrule. I bought weather proof and ultra violet ray resistant "O" rings, so they would last. When installing them, the "O" ring gives you some flex and you can tighten the new ferrules snuggly so they don't rattle around in the door. While this may not be the original way they were done, it sure does give the installation a more professional look.
Hope this helps!
Joe
