Power brake systems using "hydro-boost" may leak power steering fluid from the hydro-boost unit located behind the brake master cylinder. Replacement of the hydro-boost unit is the common repair to correct this concern.
Car Problem Reports
GMC Suburban 2500 Power Brake Units May Leak Fluid From Hydro-Boost Unit
GMC Suburban 2500 Problem
Visitor, 1997 GMC Suburban 2500, 165,000 mi
I lost power steering and power breaks. Everything works with "Armstrong" steering and breaks, but there is no way my wife can use it this way.