Does anyone know what kind of differential fluid I need to put in my 05 Cayenne S; I drained it by mistake, long story, now I need to refill it. The dealer said I need three liters at $78/liter; but they did not tell me what brand or weight it is...

I just called the local Autozone and they told me that I need "85w-140" differential oil for about $6/quart...why is the dealer's price so much more? is it an special differential oil? or just a huge markup?

Thank you.