Leking Brake Fluid

Early this winter, traction control, abs, parking brake ( red exclamation with circle and parantheses), and brake warning light ( yellow exclamation with circle and parantheses) turned on. Those came and went then they stayed on for good. I knew this rear wheel sensor was acting up, and I had the same lights, and I thought it was that again because I got the same lights last year.

One time, the parking brake sign/light turned on for a min or so when I put the car in ready, then the other lights came on. That's when I realized I was losing brake fluid. My cup under low.

I topped it; it takes 1-2 months on average for it to empty (hard to tell, I guess it depends on usage); I could swear I heard recently drops fall inside the bay on metal as I was stationary and depressing the brake. Recently, I heard the booster motor whirl for like 30-60 seconds or so. I topped it then it started doing its normal thing, short bursts. When I top it the lights go away btw and everything works fine.

This makes me think the leak is at the brake booster or bellow it since it was so empty that the engine was running without compressing anything.

I can't confirm 100%, but at least when the lights are on, the ABS (and of course the cruise control) are not working. Not sure if the ABS is working when topped off - but off the top of my memory I think it did the last time snow fell; I wasn't trying to actively slide. Early in the winter I did a few rounds in the parking lot and ABS was engaging.

Of course I will address this asap. I am aware that if that tiny gap suddenly bursts I'm SOL right away. Pulling codes tomorrow. Some early questions:

1) Are there any known regular failures that I should start with/ look for?

2) Is there a possiblity that one of the pipes burst and that the booster/abs control are fine? Given that the brakes work normally once I top it off. Or when this happens the brake booster needs to be replaced.

I'm not 100% sure yet how to troubleshoot this to pin point the issue. Once I open it I guess it will be more clear.