Hi all, I'm a new member to this forum from L.I., NY. I drive a '94 E320 w/90K on the clock. I do most of the work on the car myself as a hobby. My present problem with the brakes is this; when parked overnight or extended period of time, the brake pedal drops to to floor, one pump and the pedal pressure is fine. On extended highway drives, the pedal sometimes also drop very low when I step on it by a toll booth or exit ramp, one pump the pedal pressure returns to normal. This been happening several months. Master cyl seems fine, it holds pressure while stepping on it hard with engine off and with engine running. Brake booster seems fine, normal pressure needed to stop car. I bled the brakes a few months ago, pedal pressure fine a few weeks, then reoccurring problem. I then changed the front rotors, pads, rear pads, flushed brake fluid; pedal fine for a few weeks, now it's dropping again. Anybody got comments on this? It's driving me nuts. Can't figure out where's the problem.