If you recalculate normals again it will reverse the effect. Basicly you need to stay away from doint it after you attached parts.
In my moddels works i would cut a lot of parts to fix the shadowing, all is left after attaching all - to smoth, and you are done.
If you leve that dark part as it is, it will look the same ingame.
I am ussing russian on my ZM so words can vary. You need to cut that part separate and go for surface>normals>recount or calculate. If not working, you gotta cut only flat top proection and do the same stuff, but it will look off.