Carrier/rack problems of the 2009 Chrysler Aspen

Have taken car in to Chrysler dealership with regards to noise. Car making whinin noise while driving. Initially advised rear pinion seal leaking. So no fluid in rear differential unit. I stated rear pinion nut was a recall and if nut had been replaced, how any why did fluid leak out? rear differential service performed and fluid added with service at my expense. Advised noise would go away. Took car in again almost three weeks later, as patiently waited for noise to go away, now told rear differential carrier bearing are worn and $2000 to fix car! all of these rear differential failures are the fault of the rear differential pinion nut.