Disco 2 Steering box noise

I'm getting a clicking noise from within the steering box which you can hear quite loudly even from within the car. Could this be a symptom of the box needing adjustment on the top screw to remove play? I do have quite a bit but the adjuster is seized in the locking nut, it's been soaking in penetration fluid for weeks and I tried to free it off earlier but snapped my cheapy torx bit in the adjuster so I'll order a decent one in a socket and give it another go.

The locking nut complete with adjuster does undo but from the diagrams I've seen online I can't work out if I can unscrew it all the way or if I'll either get covered in PAS fluid and knacker a seal or the adjuster is somehow fixed into the sector shaft?

Here's a video of the problem taken after I'd replaced drag link and track rod, clicking is definitely inside the box.

adjuster is secured to sector shaft, if it is the box making that noise and not a bottom swivel ball joint replace the box pronto

Thanks James, definitely not a ball joint so it looks like a new box then. I guessed it might have to be but was hoping for some miracle (and cheaper) fix. Ah well, may as well change the two rusty pipes at the same time and give the intercooler a wash out while it's in bits.