Series 1 Diff groans on deacceleration

Garage LR specialist just fitted new rear diff oil seal and flange now groaning noise on deceleration checked oil less than half pint in diffs ( they were supposed to refill) two pints now added. Oil that came out was grey!!!!!
Do you think diff now buggered. Any suggestions please not a happy camper as usual garage doesn’t admit any responsibility.
Thanks MTB

As diff still works carry on using but life may be limited, depends if the grey in the oil came from gears or bearings.

Still groaning with new oil added? Agree with Tottot; you may just have to suck it and see...

Is grey oil not caused by water in oil? check axle breathers are not blocked.
Try a magnet in the oil to see if metal particles contained.
Are you sure the noise is from Diff? The intermediate gear in transfer case is helical and slides between the copper faced washers on drive overrun the facing wears off.
What's the oil like in transfer case?