Lets see if you guys can help me

The steering on the XJ has been lightly knocking during some turns for a while now.
I finally just had a proper look at the MOT advisories, and one of them is that the "Drop arm bottom ball joint" is worn. Am I right in thinking that is the same thing as the drag-link end??
If so, might it be likely that that's what's causing my steering knock? May it also create play in the steering?
Finally, how hard/expensive/urgent would that be to fix?
Cheers!
