2002 Ford Explorer Master cylinder

About a month ago I had my brake pads replaced at the deatleship. After driving it for a couple of days, I noticed the ABS light was on, so I called the dealership. They said not to worry. Do I didn't. The ABS light has gone off and on a few times since then, but no other noticable change except a pretty constant squeeky noise from the brakes (started maybe 3 weeks ago). So after about three weeks I brought the car back to the dealership to have a look. Now they tell me I that I have to replace the master cylinder because it is blown. Does this sound right? Shouldn't they have told me that ABS light might be a warning of leaking fluid from the master cylinder? Julie