This is the machine:
And here is the 45-90-45 locking mechanism:
There is rotational play in the arm even when the wedge locking lever is firmly located, and this is the case for all three positions, even the rarely used left mitre. So I think the problem is in the lever wedge, not the column cutouts.
The wedge does not bottom out radially, ie there’s a good gap between it and the bottom of the column cutout.
Using a marker pen, I can see the contact patch is at the lower edge of the wedge, so the play is at the top (greatly exaggerated in diagram - it’s about 0.1mm each side:
Should I be marking the contact patch and filing to improve the fit, or perhaps run the wedge surface on a diamond plate, with pressure on the high end, to maintain flatness, or something else?