My 1995 C280 has 95k miles on it. I had completed a 30k service at the 90k interval, except I had not completed the fluid change of the differential. Today I purchased some Valvoline Gear Oil, a synthetic blend. I left my car next door at the mechanic while I work to change it.
I have a few questions... what are the benefits of changing the fluid? The bottle even said Improved Fuel economy? Is this so? Probably VERY minute I'm sure. I wonder how dirty the old stuff is...

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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!)