Printing circle in a circle, Skp drawing problem?

Im making a Drone and printing my own arms. Ive gone through many versions and now Im working on a clamp arrangement where 2 pieces are bolts down on 3 carbon fiber tubes. In the middle of this will be the motor, which has a large central hole and 8 small ones to screw it down with.

Ive redrawn this part many ways and times, but each time odd problems occur, sometimes when saving in Sketchup but usually when printing, eg the central piece is floating and unattached. If I repair the STL file with online tools it prints but fills in the holes, which means I have to drill them out again when printed.

Ive attached the file, can anyone look at it and give me some tips?cf out arm clamps v5.stl (167.7 KB)

Can you try removing the face marked in blue before creating the STL?

Also, you might want to use the “I want this model to be Printable” to create a STL file from the 3DWarehouse