I happened across this dead thread tonight. I had the same problem once on my car, a 1993 300D.
The problem with mine was the clip broke that holds the washer fluid tube out of the way when you close the hood, so it was simply getting pinched every time I closed the hood and that resulted in no flow.
Zip-tied the line back in place and haven't had an issue since... well, until today when the nozzle burst into flames, but that's another thread