Quick summary:

Car has about 3 year old brake system, every single component sans the proportioning valve was replaced. Drove it less than a week ago, brakes worked perfectly. Yesterday went to move the car, brake light was on, and I could tell something was wrong, car still has brakes but feels very weak. Pedal is firm when the car is off, but when running it has a lot of travel before anything will happen. It still stops itself, though not well enough to drive normally. It has mostly been sitting in those 3 years.

Opened the reservoir, front was full to top, rear was nearly empty. have been all throughout the car, it is not leaking brake fluid from anywhere, unless I am missing something. I am not the one who did the brakes, and this is the first time I have ever checked the fluid, yes, stupid. I filled the fluid back up, went to bleed both rear drums. As soon as I opened both bleeder valves fluid immediately poured out, was very easy to then get fluid to come out with no bubbles doing bleeding process. Topped reservoir back up, has not had any change. I guess its possible the fluid was always low, it was not empty, fluid level was above the bottom, but just.

Could anyone give me some advice here? Thank you.

 

So, you don't really know what they did or didn't do, and being that it was three years ago, any warranty is likely expired.

The rear brake reservoir is closest to the boster. Sometimes, it leaks into the boster. You may want to check there.