When I was having some squeeking noise with my wiper and decided to clean it, I learned how to manually move the wiper blade (I think this is what I did, I can't recall!)

Turn the key, turn on wiper and then immediately take the key out of the ignition so that the wiper has moved and is not in the parked position. Now if I recall correctly, you can now move the wiper 1 full cycle... you will be able to move it from the point that it stopped, all the way to the passenger side, and then back into the resting position on the driver's side. I am pretty sure this is the correct procedure. Give it a try and let me know.

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)