If you want to save money you can clean and polish the assembly. There are two ball joints, left and right as you face the windscreen. My left had one seized.
Take the whole assembly out and disconnect the arms from the motor.
Move each arm to see which one is seized.
Remove the circlip and O ring, and put in to a vice. It will take some doing, but it you keep twisting it to and throw, and it will slide out.
You will then be able to see all the corrosion which has caused it to seize.
Remove, clean, polish and then refit.
I put some copper grease on the pin, and a Special grease for the rubber o ring.