I can see there is some sort of set screw comming in from the side, but none of my allens, ISO or metric, seem to fit. What size specifically is it? Or is it something else? bristol spline? Straight blade screwdriver? I can't see down that tiny, deep, hole...

It is an allen head set screw . . . not metric. . . yours might be dinged on the edge. . . keep trying. . . about 1 or two sizes up from the bottom of an allen wrench set. . . You will get-r-done. . .

try a 1/16 or 1.5 mm

Thanks Glen, that was the ticket. I also figured out why my first attempt with a 1/16" didn't work, the tip of the wrench was bent... I tried a ball end Allan driver I have and got it.