Hi and welcome to the forums. I presume you mean both the passenger and driver seats? Mine was a loose connection under the driver seat, not the passenger. It does seem daft as when the car is being driven, there is always someone at the wheel and I thought the sensor was there to determine whether or not to deploy the airbar?
1. Not sure if it's the same as on mine, but some you can unplug and squirt a bit of WD-40 into the joint
2. The root cause on mine is lack of slack. I removed mine from the seat frame so that it had more slack and the problem (touch wood) is resolved. I just need to loosely cable tie it back to the frame at some point
3. No reason why you should not solder the joint if this is where the problem lies
I also feel more comfortable disconnecting the battery when I've got my head close to something designed to explode!