now that summer has returned i have noticed my "squishy brake" problem has also returned, where my brake pedal will begin to sink to the floor when i apply the brakes and i dont brake as well, and i have to pump them a bit to make me stop well, i do not lose brake fluid, however my brake fluid is a odd brownish color now... i am thinking perhaps my brake lines are getting to hot and are expanding as i apply pressure to the brakes?

anyone have any opinions on this? and if it is from overheating brake lines, whats the best method to cure? buying a metal brake-line system?