1995 Chevy Astro brake system failure

I purchased a 1995 chevy astro van in june of o7. I took it to midas for a brake check and they ended up replacing much needed front idler arms. I was then told that the rear shoes needed replacing and the front discs were fine. I have since put 10,000 miles on the vehicle and within the last two weeks the brakes have failed. Upon taking it to the shop within five minutes from pulling it in to the bay the gentlemen came to me with the bad news. Someone had put power steering fluid in the brake system. He said the entire system would need flushing and all seals replaced for about $2000. My questions are: What really has to be done? How do I get a parts list? Can some of the parts be used? How did midas change my back brakes and top off fluids without entering the system as they stated when asked. I have synthetic oil. It hasn't been in any shop. I know better.
Thanks Don