2000 ML320 Differential
 

I am the owner of a 2000 ML320 and was just told I needed a new front differential. Car has 61,000 miles and was never driven off-road. What can cause this? Anyway to get the part used/lower price? The car is with Mercedes Benz and they are asking for $3,500 to fix it, no other option.
Any advice?

Most likely cause was previous replacement of the pinion seal!

You can find used ones for around $1000...Takes 3-4 hrs to install..