Hi Steve,

re:
> Bonus points for a means of detecting the problem, the model looks fine in Blender and MeshMixer.

To detect this problem in Blender, in Object Mode or Edit Mode go to the Overlays button here:



Enable "Face Orientation" :



Now forward facing polygons will be displayed in blue and backwards facing polygons will be displayed in red:



With a well formed solid object you should only be seeing all blue, if there are any red areas those don't have the proper orientation.

In MOI you should have just one object that selects as one piece and when it is selected the object type indicator in the upper right area of the window should read "Solid" and not "Surface" or "Joined srf".



- Michael