1991 Chevrolet Caprice Question: POWER STEERING FLUID IN MASTER CYLINDER

a complete system flush may be required but you could try this first to save time and money.you'll need a hand held vacuume pump and a 32 oz bottle of valveoline dot3-4 synthetic brake fluid.remove all the fluid from the master cylinder and wipe it out with a rag as good as you can then fill it with your new brake fluid,then bleed about 18-20 oz's of the old fluid from the right front,then 12-14 oz's of old fluid from the left front,keep topping off the master cyl with the new fluid so air doest get in.use the whole bottle and test drive it again.hopefully the powersteering fluid didnt collapse the brake hose.

Sounds like you will need to replace...nearly everything that is rubber....all seals, hoses, through the whole system. Oil contamination in your brake system is absolutely catastrophic, and what you are experiencing right now is showing clearly that the oil has reached critical areas.