 I like to change master cylinders every time I do an ABS controller, simply because here's a 15-year-old vehicle that's had reasonable brake fluid flushes, but not enough. It's always not nearly enough in my mind because the fluid's discolored. There's a certain amount of grit and particulate at the bottom of every master. I don't care. It just collects there. It's the course of normal breakdown of fluid and operation.