Well I've been doing this (lube) kind of stuff for a very long time and it's a rip. True some times the system can get contaminated, but that takes such a long time and you would know if the break system got contaminated because the break booster would fail. I've ran several breakchecks. Break fluid is curosive anyways and can cause rust. While flushing the system wont hurt it is not a have to. Same with powersteering fluid flush. Plus you would be able to see if you need to flush these. They do not get the heat that motor oil gets so they will last longer then the car. Put it this way, if your radiator fluid is good for 60k you can beat the break and power steering is good for far better.