Hello im from Sweden with a Legacy 3.0 07 and having the same problem as you have.
See this is a old thread and as usual no conclution what the problem was.
So are you still here and can tell what problem you had?
I have new tyres,rims , rotors , calipers , brakecylinders , wheelbearings struts springs ...well all those parts and bushings are new in the front.
Well not the cv axles.
When going straight i must hold the steeringwheel about 5° left, if i let it go my legacy will go right.
If i drive on the opposit side of road (left) my car going straight if let sterringwheel go.
I have noticed my legacy is very sensetive of how much the road lean.
If driving slow and turn left and let go it will center as normal.
If driving and turn right it will center slow when letting it go.