Does a leaking drive shaft pinion outer seal on a 1998 Jeep Grand Cherokee cause the internal rear differential pinion setup to lose its preload and need to be replaced.

Is the following Jeep dealer guidance correct? The seal where the drive shaft pinion enters the rear differential leaks.  It may have leaked for some time as it has sprayed the underneath of the body as the fluid spun around on the drive shaft near the bearing.  The jeep dealer says I have to change the outer pinion seal, and pinion bearing and a few other internal things because the pinion lost its preload since the seal leaked and lost fluid while I was driving. I find it hard to believe a mechanical function would be lost due to leaking fluid.
  About four years earlier on another same year 1998 Jeep Grand Cherokee with a similar leaking rear diferential pinion outer seal all the same dealer did was replace the seal and all was fine.