Camry :: Master Cylinder Leaks Caused Faint Squeaking From Brakes

I have a 2004 Camry LE with 214,000 miles on the clock, and this car has had needed maintenance pertaining to the braking system ever since I bought it in January. Let me give you some background on past issues/maintenance before I dive into my current issue.

During the test drive, the brake pedal felt extremely soft/spongy, having to travel a lot farther than any other car I've driven (even my father's full size pickup had stronger brakes). My dad dismissed it just being the way the car was. In hindsight I would've walked away or slept on it, but let's just say I was pressured into buying the car right away.

We took it to my trusted local mechanic a few days later for an overall inspection, and he said the front brakes/rotors needed to be replaced. He said the rear brakes were thin, but could be replaced later down the line. So we replaced the front ones, expecting it to have some improvement. In reality, the brake pedal force was still the same as before.

A few months later, after hearing faint squeaking coming from the rear brakes, the brake light started to illuminate intermittently. That's when we decided to replace the rear brakes/rotors. After we replaced the rear brakes, braking motion was dramatically improved, and I did not have to push the pedal very far to achieve adequate braking power. It was great,while it lasted.

It gradually started to go back to the way it was, which is really disappointing. After growing tired of the problems, I decided to check the brake fluid level in the reservoir, and it was practically at the minimum line! Figuring it was a brake line or master cylinder leak, we took it again to my mechanic to have him inspect the braking system. Much to everyone's surprise (including my mechanic), there were no leaks to be found and he told me to come back if it gets worse or the brake light comes on. HOWEVER, when I drove it home from the mechanic, the brakes felt the way they did when he put the rear rotors on. On the service record, it said he just looked for leaks and readjusted the rear rotors. This was about a month ago, or at 209,000 miles.

However, as before, the brakes slowly started to loose their "bite" again and sure enough, the master cylinder had lost fluid; albeit not as significant as before, but enough to require topping off. In addition, whenever I'm decelerating on the freeway (from let's say, 75-60 MPH), the wheel shakes as well. This wasn't really present before.

My patience is running thin with this car; we've easily spent half the value of the car on maintenance.