27. I put some blue threadlock in the hole, added some washers, and screwed the hex bolt back in.

Then I re-attached the forearm bone with the cross-wise (lower) nut-and-bolt. For good measure, I put the plug of silicone back in the bracket. It reduces the volume of air in the arm, and therefore of corrosive water vapor.

By doing 'half a job', in other words by not attempting the impossible (like cleaning the socket for the hex bolt and extracting the aluminium plug, as described in the first photo), I got the job finished in reasonable time (an hour, maybe). However, I spent at least the next hour cleaning the black metallic muck (from inside her arm) from where my fingers had inadvertently rubbed it into the outside of her arm.