Thanks to all. The verdict was to change the bearings, so I ordered 5 inexpensive bearings from VXB (4 for wheels plus 1 for brake hub). I put the 3 rear bearings in along with my new K70 3.50 tire. Reassembled all.
The test drive was fine, but afterwards I noticed the spindle had slid aft about 1 mm on the right side (right chain adjustment cam plate was no longer touching the post). I figure this is because I did not tighten the castle nut enough before putting in the cotter pin. It was not very tight when I took it off, and I don't know how tight it should be. The workshop manual says, "Retighten the castle nut fully such that the split pin hole is aligned," but what does that mean? Is there a rule of thumb or torque setting for the castle nut?