[phutyle]

I was never able to find an OEM pad/kit, and this Rejel one is the only one I could find to fit the car. They seem to make pads for pretty much ever car. Maybe they are the OEM supplier, I don't know. But that pad setup is what the rain sensor should come with. I've seen people on forums posting that they've used clear silicone sealant instead, but I have no idea if the qualities of silicone sealant(refractive index, etc) are suitable for the sensor. This pad is, as the auto wipers now work 100%.

Edit: Actually, from some things I've read, it seems the pad isn't available as an OEM/Volvo part at all. The OEM solution is to replace the entire sensor if the pad is missing/defective.

The kit comes with a syringe of liquid gel, and the pad. You put the sensor on a flat surface, and slowly flood it with the gel, until it comes to the top of the lip (and making sure none goes into the hole on the left/passenger side). Tap it to release any bubbles, then leave it to set until it becomes tacky. Then you put the pad on, and refit.

I assume the 8 truncated disks are the sensors. They're arranged in a ring, and black material on the windscreen is absent over them to let light in to them. The black bit on the windscreen in the middle is just cosmetic to cover up the area that doesn't have sensors. I'm assuming the system works by sensing the light that is bent through raindrops, due to it having a different refractive index to the glass - which it why the material between the sensors and glass is important. If it has a refractive index that's similar to water, the sensors are going to think they're detecting a wet windscreen all the time. Or it's going to negatively affect the detection of actual water. This is why mine didn't work without the pad - the air gap between the sensors and the glass did not allow the sensors to take a proper reading of the light coming through the windscreen (and water if present).

There's also a small hole in the sensor on the passenger side (with a lip around it), with a corresponding hole in the black material on the windscreen. It doesn't get covered by the liquid gel, and the pad doesn't sit over it when seated properly. So it has an unobstructed light path through the windscreen. I assume it too is a sensor, maybe taking a reading that is then compared to the other sensor matrix. It's hard to see on your photo if it's covered in gel. It shouldn't be if it is.