I had a similar problem with my mono-blad wiper.
The cover snaps off real easily, and just needs to be lubed. I just used some sylicon spray, but I think a grease (preferabely MBenz grease) would be the right way to go.
I don't recall how to snap off the covering, but it's fairly simple.
There are instructions how to do this somewhere in the Archives. Use the SEARCH function, and type in "wiper lube" or 'slow wiper' etc, etc; many results and info should come up.
2006 E350 w/ 155k miles (Daily Driver)
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!)