Nonmanifold edges / self intersecting curves / Boolean diff failed

I’m about to hand a project back to a client due to the above. Is there any way to troubleshoot these issues beyond being told by Rhino there are issues? I’ve checked everything I can think of but I still get these warnings and my Boolean operations still fail.

A related question - is there a more robust version of Join in Rhino? I’ve joined a handful of surfaces but when I extrude them, I get 3d solids based on the unjoined parts. The surface isn’t planar so it doesn’t help me to dupborder and create a new surface.

Pulling my hair out … thanks for any advice you’ve got

Well there’s ‘joinedge’ but it’s recommended not to use it. Problems often arise.

Hi Arail - running Intersect on the objects and inspecting the resulting curves is the first line of inquiry as a rule if Boolean operations fail - but send your file to if you don’t sort it out, or to me via private message, and I’ll take a look.