Just a thought, if the barrels are anything but ceramic, whatever you do to fix them will be very temporary. I have gone to all ceramic inserts or actual tips and I've been using several different models for years now without any problems. Bite the bullet, get rid of those metal tips and get the ceramics, you won't be sorry you did.
Just my opinion. I tie almost daily year 'round so they get a lot of hard use.

kelly.