Our 2005 Forester has a similar problem--when it is less than 20 deg F, you have to use an ungodly amount of force on the brake pedal to activate the brakes until it warms up or the brakes have been used a few times, then they are normal. I have had the local Subaru dealer look at it several times and even suggested to them that it was a check valve. They replaced other brake parts and the problem continues.
Does this model have a check valve that can be WD40'd or replaced? Seems like something I should be able to do myself but I could also use a diagram showing where this is (assuming we have one!)
Many thanks!
Bud