Normal map seam on curved object

I am having problems with a normal map seam on the hair for a character I am designing -- I sculpted a high poly mesh in Zbrush, retopologized and UV mapped it in 3d coat, exported it as an OBJ, and baked normal and color maps for it in XNormal. Trying to solve the problem, I found a Unity 3d Tangent Space plugin for XNormal, which I used instead of the default Tangent Space to bake the map for the material described below. This has not resolved the problem. Furthermore, I am calculating both normals and tangents through Unity, with a smoothing angle of 120. As possible other options, on import I have tweaked the smoothing angle of the mesh and checked split tangents on and off, and still I haven't been able to resolve the seam. I have also tried putting an inline seam on the mesh, to no avail.

I am not sure what is going on here, and I have had this same problem several times on curved objects as well. I can usually resolve the issue for straight UV seams by making sure they are parallel on the UV map, but if the UV seam is curved, I cannot get the seam to go away.