Torrential rain in September on the M5, caravan in tow and the wiper linkage decided to come adrift. It was the passenger side but then jammed the mechanism and I lost the wipers all together. Really it couldn't of happened at a worst time. Very fortunately their was a service road which I managed to pull into off the M5, I removed the passenger wiper in the torrential rain which freed up the mechanism and I managed to get home.
When I stripped the mechanism down, this must of happened before because the seal on the failed linkage was damaged.
I ordered replacement linkages and arms, their is a kit on Ebay. You must throughly clean all surfaces (really important) then re-lube, I used silicone grease and clipped the new linkages back in place.
In my case it looks like this had been taken apart and had been contaminated with dirt and probably not re greased, as the dirt had eroded the nylon ball cup and it just popped off.
Its a pretty simple job, you need to remove the wipers and plastic bulkhead cover at the bottom of the windscreen then the whole wiper mechanism is accessible.