Hi I'm new to this forum and have been reading this thread with interest.
I have experienced the same problems with the low level warning and headlight washers that don't spray. I told a friend about the problem and mentioned that it was probably a conductive sensor that was used for the measuring. He then suggested to increase the conductivity of the washer fluid by adding a small amount of salt...
I tried with 1/10 of a teaspoon in half a cup of water - stirred it well until it was completely dissolved and then added it to the almost full washer fluid reservoir. After 5 km of driving the headlight washers started working again and when I turned of the ignition and turned it back on the warning light had disappeared and it has stayed like that since
I know this is not a solution to the real problem being a conductive sensor with incorrect sensibility but I hope you can use this information until BMW comes up with a permanent fix.