>>9081727I do repairs for these joints. What you need to do is drill a hole in the center of this back to reach the screw, if there is one. I've not touched a Kabuto body so I'm not too sure where the screw is, but on Showa Riders its covered by a noticeable panel.
The joint itself is basically irreparable. You'll need to UV resin or use some other form of plastic to make spares.
I've done these joints for Skyrider, V3, Rider 1 (THE FIRST), etc.