2008 E350 4Matic Differential
 

My dealer says the pinion bearing on the rear differential is responsible for the growling noise on the road. As he won't repair - only replace (for many thousands of bucks) - does anyone have a reliable source for a rebuilt unit. Or, a recommendation for an independent shop that can repair my unit somewhere in the southeast. I am in Memphis, TN.

Thanks for any and all suggestions.