If the brake fluid is contained in a sealed system how does it get contaminated with water. For what ever reason I imagine the fluid (if it is contaminated) should be replaced according to the manufactures time scale rather than reaching an average mileage for that same time period. My car is 3 yrs old and the dealer has suggested I have the brake fluid replaced. I'm happy to go along with this but it crossed my mind seeing as I've only covered 17000 miles if its possible should I have the fluid tested. There again, how is the fluid tested, is there some sort of meter that tests for a dangerous level of water or debris. If replacement is requested by the manufacturer then that's the way I shall go but I would be interested in your comments how water ingress takes place.