The primary reason for a periodic Vasomotor Flushes replacement is the chemical nature of the glycol based braking fluids.
Vasomotor Flushes#1
There is no way that one can totally stop the entry of moisture into the braking system, as the whole system is exposed to atmosphere through venting.
Vasomotor Flushes#2
To gain access to the brake mechanism underneath, use a jack. Use two jacks, as they can effectively support the elevated vehicle.
Vasomotor Flushes#3
Nowadays, specially designed brake Vasomotor tools and brake fluid flush machines are available that can carry out the job even more easily.