This is from the info I and Tom posted and the links are on Pg one of this thread -- a partial posting of the prior info ---
Brake Fluid Preventive Maintenance
Many experts have long recommended changing the brake fluid every year or two for preventative maintenance. Their
rationale is based on the fact that glycol-based brake fluid starts to absorb moisture from the moment it is put in the
system. The fluid attracts moisture through microscopic pores in rubber hoses, past seals and exposure to the air. The
problem is obviously worse in wet climates where humidity is high.
After only a year of service, the brake fluid in the average vehicle may contain as much as two percent water. After 18
months, the level of contamination can be as high as three percent. And after several years of service, it is not unusual to
find brake fluid that contains as much as seven to eight percent water.