So, as I read the recall letter the pinion nut loosens because the splines on the pinion gear are cut too small or the companion flange spline is too large and because the fit is loose, the pinion nut is over stressed and loosens. Since your rear axle is being rebuilt by the dealer to solve the problem, it is not just an issue of a poor quality nut This is an expensive recall for Chrysler and they probably had to fill the pipeline with complete sets of parts so that if a problem was discovered it would be fixed right the first and only time. Seems very responsible to me