Rear differential leak

[John]

Got a question. I've had my car about a week. I've been watching all the typical areas for leaks (front and rear main bearing leaks, trans and differential). I took the car for a short spin Saturday and on Sunday, noticed a small pool of oil under the rear differential (size of a pancake). Prior to Sunday, I was not getting any leaking from this area.

Will those seals just fail?

What is level of difficulty to replace?