The brake problem could be several things. I would say pull the rear drums off and inspect the rear wheel cylnders. If they are not leaking (rear wheel cylnders), inspect all the brake lines and calipers for a leak. If you don't find a leak, the master brake cylnder has probably failed.
I have a 1992 SSE. The rear wheel cylnders usually fail about every 50k miles and the master cylender every 100k miles. The shoes and pads have always lasted at least 100k miles and I have never had to replace the calipers. I always flush the entire system every 50k miles. Go figure.
My son just replaced the rear wheel cylnders, shoes, master brake cylnder, and flushed the entire brake system. The brakes feel better now than when the car was new. We bought it new Thanksgiving week 1991 and now has over 231k miles. Still has the original engine, transmission and CV joints. I don't have to add oil between changes and run the oil 7500 miles. I love the car and the HUD!