2003 Buick Regal Brake Issue

So my issue is I was driving to work one day and lost all pressure in the brakes, with the brake light coming on.
I checked the fluid which had an almost half full reservoir and added more as a precaution.
Not driving for a few days I noticed the Fluid was down a bit, so I suspect a leak.
I was wondering about another part is that I pumped the brake up when I was powered off and the brakes maintained pressure fine, turn the car over and it’s back to going straight to the floor with no pressure.
Is there a possiblity that it’s something worse, like a solenoid or something, not that any leak is good.

More like a master cylinder. Under $100 if you do it yourself.

Remove the brake booster vacuum hose from the brake vacuum booster.

If you find fluid inside this hose, the brake master cylinder is leaking fluid into the brake booster, and it’s being sucked into the engine and being burned.

The reason there’s no smoke out of the exhaust is, the catalytic converter hides the smoke the same way as if the engine starts burning oil.

Tester

Both good posts.
If you do the job yourself, be sure you bleed the new master cylinder on the workbench before installing it. Instructions should come with the MC. It’s a very simple process, where tubes are connected to the MC outputs and run back into the fluid reservoirs in the MC. The reservoirs are filled and the MC pumped until no air remains. What you’re actually doing is pumping the fluid in a closed loop round-and-round through the MC to purge any air.

Thanks. I will try and see if the that’s the issue in the morning. It’s a tad too dark to try anything tonight.
Thanks again