Trouble creating a solid extrusion or push/pull with this imported Rhino Object

[mcobb]

I'm having trouble getting the linked file to create a solid extrusion.  Any help is greatly appreciated.

https://a360.co/2Ol2cDo

Mike

[lichtzeichenanlage]

A simple method to find the problematic area is to draw some line thru the sketch (check screencast). By doing this, it looks like, that the marked spline is the problem. Perhaps you can recreate it.