I've bought a large clamp to help the disassembling, the belt clamp couldn't provide enough grip, but I found that I was wrong, even this clamp did not quite work out.
The problem is on my arm, leg. I step on the black PST body to fix it in place, and rotate the PST etalon with the clamp, but I found foot/leg is not strong enough to fix that. Then I put the black body in a gap between my furniture and begin to turn it, however, it still didn't rotate. Even both arms are used.
I've even tried to place that black part under heavy furnitures, and turn with the clamp, but it still didn't move a bit.
Let me see if I have any further way.
See some photographs below, it's quite heavily scratched, I avoid using excessive force, for I think this might hurt the etalon:-