Its indeed a strange adjuster.
Looks like a metal fatigue issue. What is that inner thread size that snapped?
M14x1,25 or M16x1,5?
Most coilovers use a different design (same as kw/GC etc), so this kind of style:
Where yours is similar to this I think?
I think this type of adjuster only fits on the bottom, so on the control arm. that constantly changes angle, so forces are constantly wobbling from one side to the other. If it would sit on the top, those shifting forces are more equalled out in the spring I think.