The swinging arm (driver-side) windshield wiper mechanism used by Mercedes for ML W164 and R-Class W251 models (at least), has the tendency to break.
The most usual failure point is the bearing that connects the anchor arm to the motorised arm. The bearing splits apart, causing the arm to become free and move erratically. When it breaks, it’s usually getting in the path of the other wiper, in addition causing damage to both, depending on your luck.
The root cause might be the placement of the windshield sprinklers. When having nozzles misaligned, they can spray water directly in the bearings with the help of the “protective” plastic cover of the bearing mechanism, causing it to rust with time and help of the cleaning agent.
Cost of a new wiper arm at Mercedes is around 80 EUR. It might not be on stock when you need it to drive your car or maybe you want to fix it yourself for much less, therefore I’ll show you how you can fix it.
Connecting screws of 5mm outer shell diameter. I had a few laying around, guess from some IKEA furniture, can’t remember exactly so please leave a comment if you recognize the part.
For extracting the failed bearing:
For hammering in the new bearing:
Extractor with 2 arms (with 3 also can work) might come handy for extracting the wiper arms from the car.
Your usual tool set with wrenches and sockets for working on the car
Wiper arm repair process
The repair process is shown in the video below.
Don’t get confused by the extra bearing axle that appears in the photos, it’s from another failed wiper mechanism and I had it already (from the first car on which this failed for me). It appears in the photos just for reference.