If there are no issues with it, no need to replace it. If fluid is leaking out through the seal, you can unbolt the cover and reseal it. It does not take a gasket, but reseals with a specific caulking. There is a write up in the DIY section.

I bought a pump to get the fluid into the diff, as you cannot get the bottle high enough to pour it all in. But the dang pump did not work. I then bought a five foot piece of clear vinyl hose from the hardware store and had my trusty assistant pour the gear oil down through the tube while I held the other end in the diff. This worked a lot better and was way cheaper. Now I just need to find the receipt for the pump so I can return it.

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