Check the noise layers at full power. I'm sure you'll find one piece has a lighter section at the seam and it's counterpart is darker on it's side of the seam. Try inverting the layer on one part to see if it helps.
How does that nose 3D shape look with those colors if you take your screen shot inside of a test terrain?
Here's an earlier 352nd P-51B in the blue color you were doing for the P-51D. Not sure if this helps...http://media.ww2color.com/images/05739.jpg
The shade looks better but you still need to desaturate it. Far too bold.
The blue paint in all the reference photos look pretty flat anyway, so I'd got with that finish.
Also, that 's not a bit map seam you're pointing to, just a polygon corner, so do not mess with the noise maps in that area.
Looking better all the time I think.