Castrol Hypoy C Gear Oil 80-90 is fine. I've had it in my differential for a few years now. I checked it just a few days ago, and it was very clean.

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Don't Chrome them; polish them

Ok cool. The guys at pepboys told me a while back (I do my own oil changes now though...) that they checked it and the oil was "like water"...so it needs to be changed.

Process looks straight forward. Remove fill plug, drain anything that comes out. Remove drain plug, drain all out. Replace drain plug. Fill until it starts coming out of fill plug then put fill plug back in.

Sound right? Any other tips?

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k