I also drilled out the previously broken screw holes.
They had been filled in by someone else.
I started by drilling out with progressively bigger drill bits, 2mm, 3.5mm, 4mm, 5mm
Finally, after checking by hand with the hex spacers (5mm diameter), I found they were too toght.
So I used a 5.5mm bit and just cut the plastic by hand with this drill bit.
Here is a pic of the result :
I have just glued a hex specer into one of the holes. I will post of pic of how this turns out.