I wouldn't let the cages wear on whatever it is that they are touching. They don't sound to be the correct cages. You know you can pop the old bearing balls out of the old cages and put new balls in those cages (as long as you are careful not to bend the cages)? As mentioned, if you use loose balls (11), the grease will hold them in just fine. You are using grease (and a good deal of it) aren't you?