Swap the rotors from side to side and see if the problem follows the rotors. Although very unusual, I have seen this with rotors that have uneven thickness (one rotor thinner than the other) and also from rotors that were somewhat physically different (different metalergy).
You should also look hard at the steel brake lines. A kinked, bent, or squasked brake line can do this. I remember one (not a Contour) that showed up aften an engine swap and the engine installer hit the line with something and caused the line to be nearly shut.
