I think I might have cracked the "jumping" wiper problem! Here's what I've done. First off, I had the grease problem sorted by my dealership. After that didn't help, I brought some Bosch wiper blades, and cleaned my windscreen using a can of Holts Screenies. After THAT didn't work, I bent the wiper arms towards the screen. As a final act of desperation, I sprayed WD-40 on the linkage. The WD-40 has cured the problem! I think the linkage was "dry" and the WD-40 has sorted it (For now....)
P.S. If the WD-40 wears off, are there any other types of grease that I could use to do the same job, that would last longer?