Rear Diff is leaking oil...

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I noticed over the past few weeks, there has been a dark oil spot forming under the rear part of my X. I didn't think it was my car... so we had our garages powerwashed. Now, I can see fresh drops of oil and to me, it looks like it's leaking from the rear center diferential or whatever that is. Luckily I'm still under warranty.
But has anyone here had this same type of issue before? What do they do? Just replace a gasket or something?
Any information would be greatly helpful.
Thanks. =)