I use a 2nd cut mill file, and sandpaper. Occasionally I do break out a wire wheel or cup brush on a drill or angle grinder but not for the caliper slide rails. I guess I could... I also have a small diameter 90' straight rotary brush, like around 1" to get into the face of the hub around studs but this usually only needs done once per vehicle because if I get it clean or it was already clean the first time I touch it, it gets a thin layer of silicone grease which makes rust no longer a problem on that area, just making sure not to get it on the brake friction surfaces or lug studs themselves.