I was having the same issue, so I took it to my buddies shop. He filled it back up and the problem went away. Most likely a leak somewhere. Going to tackle it this year.
"Speak English... I am speaking Engrish..."
Steve Chang
99 Silver SVT Contour #196 (Garaged)
06 Dark Blue Pearl Fusion SE V6 (Daily)
05 Dark Shadow Grey Freestyle Limited AWD