First off, welcome to the forum.
Now then, I would check all of the fittings, from one end to the other. I would unscrew them, clean them, check them for any stripping, repair any issues, and then re-tighten them properly. Then, I would check for the issue once again. If the problem still exists I would start looking for a possible split in a line. You might also check for any leaking coming from the underside of the booster, master cylinder, or equalizer valve. I guess that would be a good start. Once you have found it and fixed it I would completely bleed all of the brake lines until fresh clean fluid runs out all of the bleeder screws. Good luck and let us know how it turns out.