Looks like an ideal project for @Andyjr1515
https://www.ebay.co.uk/itm/324583393290?hash=item4b92ad880a:g:OYsAAOSwPxNgf~ud
Unfortunately, the truss rod nut has failed out of warranty, having either come unthreaded or broken, and just spins freely in its collar. The hex socket isn’t stripped and the nut is captive, so can’t be repaired or replaced by itself. Yamaha say they don’t supply replacement necks and that to replace the truss rod will need the fingerboard to be removed, a job that’s beyond my skill level and my pocket.
Although technically “playable”, the neck relief can’t be altered as the rod cannot be tensioned, so I’m selling it for spares or repair only, it might suit someone as a project or to cannibalise for spares. Everything apart from the truss rod is in full working order and had only light, home use.
A reserve has been added since I posted this.