Rear Hub Binding - Why?
 

Hub: Powertap SL+ (6802 and 6902 cartridge bearings), 32 hole laced to Kinlin Niobium 30.

History: Bought new and put maybe 5k miles on it. Seen some rain but nothing crazy.

Symptoms: Lots of resistance and totally binds as soon as quick release is tightened. Cassette body is also super loose and can almost be pulled off by hand.

Could I have worn both the bearings and the cassette body this fast? What else could be in play?

This is from Saris. http://www.cycle-ops.com/pdfManuals/232.pdf
Sealed radial bearings should be lubed peroidoticly. 5k miles is a little long without an overhaul.

Someone left off the spacer between the bearings.

I have one, but it could be the wrong size. Gotta be it. Thanks.

Depending upon the particular configuration, there are steel washers that's part of the space in between the bearings. If any of these washers are left out, this would provide a gap for the bearing to be squeezed out of position and bind.