They are usually pretty good for a couple of seasons. The rebuild kits are much cheaper than new calipers. What does seem to wear out over time are the pin bushings that recieve the pins that slide in and out. You can get new pins but it seems like the bushings can wear out over time and get a little sloppy. This leads to excessive caliper flex which results in a soft or low brake pedal, which will feel worse with partially worn out pads. I don't think there are replacement bushings available. After 2 or 3 years throw them out, or rebuild them and keep them handy as emergency spares in case you loose a seal during a race weekend.