Fixed it!
6mm 3d version_2021Jan17a.gh (119.6 KB)
Part of the seam problem was simply connecting the wrong wire to Bounding Box.
Next was an anomalous spiral curve introduced by SrfSplit that was fixed by using Pull Curve just before it.
Then I found one triangle that wasn’t being culled due to a tiny extra “edge”. This was fixed by the yellow group, joining the edges and counting discontinuities instead of edges.
Finally, the triangles along the seam needed to be included so added the cyan group to do that.
No plugins, geometry is internalized.