Camera Ball mount has loosened from Tripod body (by 2 users)

A single nut secures the Tripod ball mount stub to the tripod body/legs. The problem is that the nut has loosened, even though it has a lock washer. I cannot fit ANY socket into the 'apex' of the tripod legs to tighten the nut. There MUST be a trick to it. I can post a picture if that would be helpful.

The Hakuba CT-8 is an extremely compact, lighweight tripod, and lacks any type of central shaft for vertical adjustment.

Thanks,
KZ