2002 Cadillac Deville Base... Brake pedal is soft, losing brake fluid but can't find anything leaking. parking brake is not working. Any IDEAS?

Does the pedal go all the way to the floor when you press it? Are you able to "pump it up" by pushing the brakes a few times to get that firm "braking feeling"? If this is the case it is the master cylinder or even something as simple as air in your brake lines.

Another thing to check is to see if the brake fluid is burnt (meaning discolored or has particulate in it). That too can be a sign of a bad master cylinder.