Whilst I fully endorse the "replace it now" advice, I managed to effect a repair on mine which so far has proved reliable in service. It involves nothing more than "parking" the wipers at the 1 o'clock position, a little grinding, drilling two holes, and assembling a nut and bolt. There is no need to remove any parts of the car and the process can be completed in about an hour or less.
0. Park the wipers at the 1 o'clock position to ensure best access to wiper mechanism under bonnet. Pull apart the ball joint (if not already apart). Tip: set wipers going and turn off ignition to obtain correct parking position.
1. Grind off the "rivet like" lip securing the top half of the ball joint to the mechanism plate and remove it. A small Dremmel type tool works well for this, albeit slowly.
2. Drill a 5mm hole through the top half of the ball joint, in such a way you can put an M4 bolt through it and the mechanism plate for re-attachment.
3. Do as above to the bottom half of the ball joint, being careful to maintain the same or similar angle. This part will have to be done in situ.
4. Take a 40 or 50mm M4 bolt, place a large (20mm) M4 washer on it and feed the bolt upwards through the bottom half of the ball joint.
5. Place the upper half of the ball joint back into place and push the above bolt through it and the wiper mechanism plate. Tip: Locate the upper half of the ball joint back into the wiper mechanism plate before inserting the bolt through it.
6. Place another 20mm M4 washer on the bolt, followed by an M4 nut. Tighten quite firmly. This should result in the ball joint and wiper mechanism plate being "sandwiched" by the washers.
7. Test wipers (with water on screen) and ensure there is no "judder" on the driver side wiper. If there is then tighten the "sandwich" further and test again. Repeat until any "judder" is gone.
8. Once satisfied with your repair apply a "nylon" locking nut on top of the 1st nut and tighten securely. Tip: M4 nylon nuts can be obtained from model shops.
9. Finally, vacuum away the grinding dust from the area below the wiper mechanism to ensure it does not leave "rust" stains after a few days.
10. A final tip - keep a spare nut & bolt "sandwich" in the car just in case the fitted one breaks. That way you can always fit it in situ in the event of it breaking again. I've not needed to yet, but best be prepared eh?
Hope this helps and apologies for no pictures. I never thought to take any when I repaired my wipers.