Changed the cores when they get worn. Its pretty easy to do.

I put Mylar rings around the magnet areas. So far so good! Just make sure to cut out the area that would cover the magnet.

Admittedly I have not tried to replace the core yet, but I need to on my SM (as it's causing air balls) and have been holding off after reading on pinside of all the trouble people had replacing theirs. Supposedly Stern used some form of loctite (at least on SM) and even people in our pinside community who I know have ten times the skill set I do, agreed it became a bigger project than expected. Maybe it's a non-issue on the newer games.

If the end gets damaged, you can pull the core out, grind and polish it flat. You need to make sure it's resurfaced square to the sides. Also if the core is mushroomed, you'll need to dress the sides. Replace and adjust. There is quite a bit of adjustment you can make to the cores.

For protection, I use mylar circles Pinball Life sells. Depending on how used the magnet the more often you'll need to change the mylar. Sparky will need it changed more often than gravemarker magnet.

Great solution, but their online store is temporarily closed (it's been closed for a while).