I've been running the ST-40 kit for 4 full seasons and 45-50 race weekends. Swapped rotors but otherwise haven't done a thing other than fluid bleeds. I inquired about a piston rebuild kit and was asked "why". I'm not having any problems but with this much use I'm getting concerned about a failure. Has anyone had a failure or used them well past 50 weekends (100 days, 500 "sessions")?