I have a 2000 Legacy GT with 120k in MN. I purchased it with 96k and during the first winter of ownership noticed that at extremely cold temperatures (15 degrees F or colder) that when I would start the car, the brakes would be very unresponsive/stiff as if there were no power assist. Drive for a few minutes, brakes and pedal function normally. I figured there must be moisture in the line, so I did a fluid flush, had the brakes checked out and was told the rears were seized and needed the calipers rebuilt, which I did. The issue is now back as we're headed into cold weather. Any ideas what is causing this and how it can be fixed?