wow, talk about low mileage. :O i assume you didn't change your brake master cylinder, correct?

my BMC started showing signs of leakage around 85-90k miles. on cold days, i guess the rubber seal shrinks so it brakes better. but when the temperature got higher than 90 degrees outside, the pedal would lose pressure. i didn't realize what was wrong until 125k miles when the cylinder finally gave out completely. so my guess is if it's not air in your system, then your brake master cylinder is starting to go (especially now that the weather's getting warmer).