Solid Inspector: Fix "Surface Border"....Manually?

Hole_In_Mesh.skp (15.5 KB)
Solid Inspector says “Surface Borders” issue…Repair Manually?
From my limited knowledge…tried scaling, zooming, edges…I’m stumped! Is this a co-planar issue? If so how to identify?

There’s no face of the end part.
A solid needs every edge to support exactly 2 faces.
If the ‘cut’ forming the end hole was ‘planar’ then drawing over one of its edges would form the face and create a solid… but, unfortunately it’s not !
However, and three edges can support a face, so it you add a diagonal line across the end it will face and become a solid…
In the image that new diagonal making the 2 faces is colored blue…

Operator Error…Must have missed the “end point” when drawing the diagonal. :woozy_face: