I want to change the rear diff. fluid on my C280. I don't know when it was done last. First of all, what is it's purpose? What will be better now that I am changing it? And it is supposed to be changed every 60,000 miles? What kind of fluid should I use? Where can I get it?
Where to start? I know it's on the rear axle, but where? How hard is it? Just drain and fill (opening the fill hole first)? No filter? I uses a 14 mm wrench, correct?

Aghh, sorry for all the questions! I plan on doing this myself, OBVIOUSLY! Thanks everyone!

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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!)