I noticed today that my brake pedal wasnt feeling as stiff as it usually is. I noticed that my fluid resevoir was low in the front half of it. The back half was full to the top with fluid. I checked all of the calipers and none of them are leaking. neither are the brake lines going to the calipers. Could this "loss?" of fluid be caused by the outside temperature change. Its gotten colder so is the fluid contracting? Also i do hear an excessive whoosh noise when i push down the brake pedal. could this be a bad brake booster? I need help ASAP because this is a daily driver and i dont want the brakes to go out on me! p.s. its an 86 svo.