I doubt that you'll have a problem with moisture absorption using any good DOT 4 brake fluid if you change it out every year or two. The exception would be if you ran the car on the track. Most tracks and clubs demand you have the fluid changed within the last 6 months to run on the track. The brake temps on the track can get much higher than anything MOST of us see on the street so any moisture would be more likely to be heated to its saturation temp. That's the other problem with water in the lines, if it boils you have steam and a compressible fluid.