Brake (and clutch) fluid should be changed periodically, since it is very hygroscopic and inevitably absorbs water, which contributes to corrosion in the system. Intervals? Yearly, at least in moist climates; every 2 years may be OK in dry areas. DOT 4 fluid is required. It has higher wet and dry boiling points than DOT 3, which is also glycol based. DOT 5 is silicone based and is not compatible with the systems on Sabres and Magnas.