I suspect that your suspicions are correct. Very few people change brake fluid often, if at all.
You are getting some good words of wisdom on brake repair. I would like to add some more; it is a very good idea after any brake work involving hydraulics, to sit in the drivers seat and push on the pedal as hard as you can with both feet. If anything is going to fail, you want it to fail in the driveway, not the freeway.
Best of luck,