Last night I reformatted the Time Machine partition that was causing the trouble. I was able to run a successful Time Machine backup – so everything seems ok now.
One thing I noticed when I reformatted was that the partition was formatted as Mac OS Extended, not Mac OS Extended (Journaled). I’m not sure if this was always the case or if somehow the formatting changed. I reformatted it as (Journaled).
The question now is whether I should still replace the drive, or whether this type of issue is software related, not a default in the drive.
