Diff oil discrepancy

Hi folks, I did ask this in the “what did you do today?” thread but didn’t get an answer - so I thought I post to a larger audience!

I changed my diff oil recently (about 2K overdue), the oil in the front diff looked like new, the oil in the rear diff was black, does this mean either the rear diff is on the way out or there is a seal gone somewhere allowing the ingress of road filth?

I usually change the fluids on time and they usually come out clean (this is the 4th service I've done on the car). Surely 2K over the service interval shouldn't make that much difference?

Black and glittery or just black???

Glitter could show signs of wear.....just black means dirt/brake dust has entered through a bust seal...

Breather in place?

Saint.V8 said:

Black and glittery or just black???

Glitter could show signs of wear.....just black means dirt/brake dust has entered through a bust seal...

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No glitter, no lumps, just black. I take it a new seal would require hub removal? Surely some oil should leak out? The levels were good.

Datatek said:

Breather in place?

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Ta Data, I'll check.

My rear diff had a failed seal - also started leaking out of hub. Oil was very dark grey, ended up replacing diff as bearings were shot.

martynv8 said:

My rear diff had a failed seal - also started leaking out of hub. Oil was very dark grey, ended up replacing diff as bearings were shot.

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Yes, dark grey is what I'd expect from water ingress, that's why I was confused by the oil being black, the stuff in the front diff looked brand new - good enough to use again!