Some years ago I replaced the wipers on my 200 with special Bosch silicone wipers. I had just used some kind of anti-water compound on the windshield, like Rain-X. Cant remember exactly what it was. Unfortunately I read too late the warning never to use any kind of anti-watering stuff with these wipers. I've never had worse chattering wipers before or since. I suspect your windshield may have been treated with something before that over time leaves a layer of gunk on the glass. I'm afraid I dont know how you might get it off. I never was able to solve my chattering problem.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S