I finally got around to taking this thing apart to see what it needed. Replaced the distributor plate, the spout clip and the rubber ring gasket that goes under the hopper. About $170 for the parts. Reassembled it and mounted it on tractor, everything moves smoothly and quietly.
One interesting thing that occurred while sourcing parts, one dealer refused to order/sell me parts for it (even though I had valid part numbers ready) because they were not for a Kubota spreader. I don't know if that is the dealership's policy or Kubota's policy, but I was able to get them with no issues from another parts vendor.