Brake pedal right to floor

[staudy]

I just purchased an 03 in June and yesterday the brake pedal went right to the floor. It only has 26000 miles on it and it happened when backing out of the garage. I put it in park and pumped it up. The fluid was only down to the seam in the plastic resevoure and I filled it to below max. There are no leaks at the wheels or around the master cyl. I started it again and it went to the floor and I was able to pump it back up. It seems OK for now but I'm afraid to drive it. Are there any issues with the master cyl on the 03's. I'm taking it back to the Ford dealer tomorrow but they will probably say they can't find anything wrong because it is working now.