Just put Bosch Icons on another car that chattered badly. But what I think helped the most was an aggressive cleaning of the glass with Bon-Ami powder, sprinkled on a moist sponge. I sponged it several times after with a clean moist sponge. Finished by rubbing with clean moist cloth, and a dry cloth chaser. Didn't touch the new wipers, and no more chatter for weeks now.

Driving on a road/highway in the rain, behind another car/truck, tosses an oil fouled brew on the windshield. I've used cheap local BonAmi, as described above, for decades.

I've never had good luck with Rain-X Spray, except on my motorcycle helmit face shield. On a car, the wipers spread an annoying film across the glass. Just my experience with it.

One time, after the C300 came back from dealer service, the wipers smeared terribly. I checked the washer fluid and it smelled like antifreeze !!! Replaced it with typical blue stuff and all was well again.

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I too use Bon Ami on the windshield and it works wonders to get rid of that oily buildup. Then I lay down RainX and all is well.

 

It's been nearly 2 months since I replaced the Mercedes washer fluid with an off-the-shelf brand. The wiper and sensor problems have indeed disappeared for good. The sensor is now very accurate. The wiper also no longer creates gummy streaks that appears at the start and end edges of the wipe. I hope the wiper blades will now last a year instead of four replacements made in less than a year. The Mercedes washer fluid creates some sort of film that affects both the blade and the sensor. I hope Mercedes will take a look into this and clarify the problem.

I used a length of tubing to siphon out the old fluid and drained it completely by operating the windshield washer. The washer bottle holds up to 6 liters. The off-the-shelf washer fluid has to be diluted 100:1. So, I used three 2L bottles of drinking water to mix with the fluid and topped up the washer container with the mixture. The level sensor worked just fine. If your windshield is already gummed with the Mercedes washer fluid, you will need to clean it first with some windshield cleaner spray and newspaper, or use Bon Ami powder (whatever it is) as some suggested.

I am not mentioning any brand of washer fluid here because I believe any of those on the auto shop shelf should be good enough to survive the market. And, probably any brand except Mercedes will work. If you are really scared, then I will advise using BMW washer fluid. My BMW E46 never has such problem. I actually do not let anyone handle my car except the dealer. I took the car to the dealer at first and they cannot solve the problem. I was then insisting that they calibrate the rain sensor or do something. They scrubbed clean the windshield and everything worked fine for just a few days. By the way, it is this that tipped me off that there is a problem with film build-up. Since then, I have been scrubbing the windshield with newspapers as some suggested in these thread. So, I kept a stock of newspaper and windshield cleaner in the booth. How can one be driving a new luxury car and had to be doing this even on short trips, and hands dirty with newspaper ink?