I will wager to say that every single W56 and W59 that has come through our doors has had a worn our center bearing retainer plate. We mic and immediately discard any piece that fails inspection. It's this very reason which prompted us to manufacture our own plates (see here and here) but we haven't released a W-series plate yet but do have plans to eventually.
Interesting, my center plate didn't show any signs of wear when I rebuilt my transmission at 160k miles.
The bearings were definitely worn out.
BTW, I used your HD W56b kit............
