i Used 75w90 Redline

So I have a 2007 C230 Sport RWD Automatic Transmission.

I contacted about 8 or 9 Mercedes-Benz dealerships and they gave me a variety of answers for rear differential fluid/oil

75w-85 Gear Oil (What The Factory Uses)
75w-90 Gear Oil
80w-90 Gear Oil
85w-90 Gear Oil

In short, you can use any of these differential fluids/oils as long as it is FULLY SYNTHETIC.
The W203 C-Class takes about 1.5L to 2.0L of differential fluid/oil (2 Bottles)

They told me to go with either
-Genuine Mercedes 75w-85 Gear Oil - Part#: 001989330312 (FACTORY) $36.00 on FCP Euro
-Royal Purple MaxGear Synthetic 75w-90 Gear Oil $22.05 on Amazon
-Mobile1 Synthetic 75w-90 Gear Oil $11.99 at Walmart
-LiquiMoly 85w-90 Hypoid Gear Oil (GL5) $13.99 at NAPA Auto

NOTE:
-The 4-MATIC W203 Takes 1.2L Of Gear Oil
-The RWD W203 Takes 1.5L to 2L Of Gear Oil

I hope this clears up the confusion in all of the forums regarding this.

very good info thank you - one update to add is the w203 4Matic (and most other w203) have rear differential fluid capacity of 1.2 US Quarts per the attached owners manual page 387

i only mention this because I just did the drain and fill of my rear diff fluid on my 2004 C240 4matic wagon and needed to know how much fluid it took.

Bringing this thread back since there is so many different variations.

I buying some items from FCPEuro and they have
1. 75W85 Gear Oil - Genuine Mercedes 001989330312 $36.09
2. 75W90 GL-5 Gear Oil - Red Line 57904 $18.29
3. 85W90 Gear Oil - Liqui Moly LM20010 $7.09

Owners Manual States 85W90 but the guys over at FCP gave a recommendation of Red Line which is 2.5X the price is it worth that much more than the Liqui Moly? Any performance difference between the 2?

Thanks for the input.

Really there isn't a huge difference. The LiquiMoly is more viscous/thicker than Redline. If you live in a region that sees snowfall, then one is slightly better. If you park your car in a garage during the snowy season it does not matter. If you park your car outside, either will work but the Redline will be slightly better since it is less viscous in cold temperatures