[solved] Intersect these

intersect.3dm (147.1 KB)
Might work for you ,but not in my domain. thanks for looking,Mark
I duplicated the borders and rebuilt. Now it intersects. All good

Hi Mark - @markintheozarks, if you use ExtendSrf to push a surface through another, use the Type=Smooth option - that way you won’t get that fully multiple knot (kink) at the extension. In this case that falls right on the intersection and although Rhino should get it, it does make it harder. In your file, DivideAlingCreases > SplitAtTangents=Yes the upper surface, Explode, delete the skinny extension and ExtendSrf > Type=Smooth. Intersect finds the correct answer from that.
(V6 gets it right, by the way on your original)