The source of the problem!

Well, after speaking (err...typing)with my friend Mark Smith, of Posey County Indiana, the center of Quicksilver innovations these days at the famous Posey Patch, he determined that when I reassembled my fan shaft and bearings, I omitted installing the spacers that go between the two bearings. This causes the inner races to be pulled together when you tighten the nut that holds the fan to the shaft. This type of bearing is designed to carry a radial load only, not a thrust load, so under improper loading, they fail. Duh, and I call myself an engineer? Thanks Mark for your insight and the spare parts. I'll have the situation all cleared up before I fly next!