I ran the Western Digital Data LifeGuard Diagnostic tool.
Running the SMART short self-test, again it ran very briefly, but the output contains more detail:
Quick test on drive 1 did not complete!
Status code = 07 (Failed read test element), Failure checkpoint = 00 (Unknown test)
SMART self-test did not complete on drive 1!
The extended self-test ran fro 2.5 hours, but stopped because of too many bad sectors. I guess that answers that question...