Mine have been awesome. Got 'em used, raced them for two or three years, replaced the seals at some point after that which was at least 4 years ago, probably longer. I'll replace them again at some point just for peace of mind but I've had no issues to speak of...probably the most reliable part on the whole car.

The closest thing to a "failure" I've seen was Mike P. and Marshall each had a caliper start leaking a few years apart from each other. Mike's was from a piston seal which he replaced at the track and carried on, I don't remember what the source of Marshall's leak was. They can chime in with the details but I don't recall either situation being very dramatic.

That being said, the piston seals are like $10 each and fairly easy to swap out. There's no harm in replacing them periodically. Don't bother with the dust boots though. They just disintegrate by the 2nd or 3rd race.