Wiper issue

I’m looking for some diagnostic help with a wiper issue. One of the front wipers on my td5 53 plate defender.
it started by both sticking and making aloud clicking noise. It did this for a month or so but now one has stopped completely and they drivers side one is working fine with the passage side one stopped and no clicking. Any thoughts on a possible fix as I guess the motor is still ok.

Splined adaptor stripped or wheelbox
Worn.

As Flossie said. Replace both at the same time, as taking the dash off twice when the other onegoes will be annoying. Don't fiddle with the grub screw on the spindle, just cut them off as you are replacing them as part of the wiper box. I had to fit a Britpart one and a genuine one as my local independent Landy supplier only had 1 genuine left. The genuine one is much better quality but 3 times the price. Both work though. Easy job to do