The reason why he posted the way he did is because this is not something that WE, the forum, would know anything about your rear diff still being useable or not. That is something that YOU have to put work into in order to find out.

Drain the remanding fluids to find out if the oil you drained has metal shavings, chunks and just looks completely silver from the metal shavings. Hell, I drained my oil before my 12 plate install and it was just silver (OEM nor any other diff oil should be silver). Good thing is that the ring, pinion and diff housing were still useable so I just bought the Weir 12 plate and assembled the rest. The shavings came from the OEM plates and for a little over a year, my car was pretty much 3 wheel drive because of the broken plates.

You can also open the rear diff cover and remove the diff inside to inspect the ring and pinion. If everything is good, you can send it to TRE and they can do the rest. Tell them about the seal and they can replace it. Seals aren't too expensive. Maybe $10 a piece.

 

Your problem is, you're not providing enough info...

We'll start with:

Was the diff whining or making any noise?
Did you drain the fluid to see how much fluid came out of it?