Use Motul 600 and completely change it once a year (at the start of Summer) and you will not any more problems. If you do have problems, it's your riding, change it more off-ten. This brake runs hot, very hot, and builds up moisture in the line during the heat cycling.
"100% synthetic, RBF 600 FACTORY LINE is a polyglycol-based brake fluid exclusively designed for races. Developed to resist high temperatures and wet-weather conditions, RBF 600 has a high dry boiling point of 312°C and a wet boiling point of 216°C. This ensures effective braking under extreme racing or rainy conditions. Couple this with its outstanding anti-vapor lock performance, RBF 600 has become a well-trusted brake fluid in many races."