I heard that you shouldn't use WD-40.
But I have been using this stuff (on antenna, wiper, etc) and it seems to work well... it lubricates nicely and does not attract dirt. I believe it's called Teflon or something along those lines. But it is a spray. Just use it sparingly I guess? Or I heard someone used 3-in-1 household oil once and it worked well. I am sure a little will go a long way. Good luck.
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!)