Has my barely-used My Book become defective ... or not?

One of my 2TB My Books failed the short and long Lifeguard Diagostics a week ago. The S.M.A.R.T. information shows that it’s had 154 power-up hours in the three years it has been in use. That is correct: it’s used only for backup and runs for about 3 hours every 3 weeks (it’s in a 3-drive weekly rotation). Drive Utilities and SeaTools also reported the drive as defective. Lightly used or not, it is well past the end of the 2-year Warranty period.

SPINRITE took 5+ hours to check the drive and found no problems. However, when I tried to copy the content to another drive, some of the files would not copy; fortunately, they were the backups done earlier the same day, so I re-ran Backup onto the new drive.

I transferred what could be copied to the new drive, then ran Data Lifeguard’s “Erase”, which I believe does a low-level format. After that finished (5+ hours), I used Partition Wizard to create the drive and do a full (not a quick) NTFS Format, which also took several hours. That succeeded, and no sectors were marked BAD.

Then, I re-ran all the earlier diagnostics that had reported the drive defective: Data Lifeguard Short and Long, Drive Utilities Short, and SeaTools Short and Generic. All of them said the drive was OK, with no bad sectors and no warnings in the (presumably updated) S.M.A.R.T. readouts.

Those positive results notwithstanding,I do not plan to use the drive for anything that matters, but am interested in other people’s experiences and opinions as to whether the drive likely is good or defective, and what may have caused the problem.