Hi Keith, that's unlike Blender to not be able to sort normals. I don't know how experienced you are with Blender, but just in case ...

Right click part to correct normals
Press Tab to enter edit mode
Make sure you have edit faces selected and press 'a' to select all faces
If you see no menu on the left side of the screen, press 't'
Select shading and UV's
Click Recalculate

That should fix any issues.

Martin
(TpwUK)