Problem: Vehicles equipped with power brake booster assemblies fail.

Cause:  Chronic master cylinder failure due to fluid leaking past secondary seal in the master cylinder bore. A defective master cylinder pushrod seal in the power brake booster allows vacuum to draw fluid past secondary seal of the master cylinder.

Solution: Replace both master cylinder and power brake unit.

Note: When replacing brake components, always flush the entire brake system with approved brake fluid from a sealed container.

Courtesy of Cardone.