Hi Lars - I suspect the main problem is that the surface is just not quite exactly tangent in that seam area.

When the offset between 2 abutting surfaces drifts away from one another, it means that they have slightly differing surface normals at that location.

Here is a kind of example of that:




I have exaggerated this above example, but I suspect that is the same thing that is happening to you, except that the normals are really pretty close to being aligned so the deviation between the offsets is pretty small.

You'll probably need to make the surface "periodic" in that direction to fully guarantee it is smooth along the seam where its edges touch. I don't right now have a tool in MoI to edit a surface to make it periodic closed, maybe I should be doing that automatically when the result surface is very close but for now if you have Rhino you can use the MakePeriodic command on such a surface to give it periodic closure which will be guaranteed to have the same normal at the start and end.

- Michael