My Rear End is Green!

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Shouldnt be LSD additive as you don't have an LSD diff. You don't need the additive with the locker.

 

maybe your truck was built on st pats day? those damn leprechauns.....

 

Sounds about right. When I did my rear diff. it was the same way, I think a lot of stuff from assembly lube and break in comes out with the first oil change. It was way dirtier than I expected. samples of oil from the second change are way cleaner, even with more mileage than I had on the factory gear oil.

 

Working in an auto shop I have drained plenty of gear oil, and when clean gear oil is in a black drain pan it quite often looks greenish depending on how the light hits it, nothing to worry about. Pour it into a lighter colored pan and the green goes away. Probably something to do with the reflective qualities or some such nonsense.
Topping it off with a different oil won't cause a problem either, 80-90 and 75-90 are practically the same stuff anyway. I would avoid mixing synthetic and dino oils though.