According to my Synology:

  • WD40EFRX-68WT0N0 - 86,272 hours
  • WD40EFRX-68WT0N0 - 86,207 hours
  • WD40EFRX-68N32N0 - 34,417 hours
  • ST4000VN006-3CW104 - 10,054 hours

According to my Synology:

Where are you finding this data? It’s not Info Center -> Storage…

Look into the S.M.A.R.T. reports of each drive.

On Synology DSM 7.x: Storage Manager › HDD/SSD › Health Info › S.M.A.R.T. › S.M.A.R.T. Attribute › Details › Power_On_Hours

The power-on hours are shown directly on the Health Info page, no need to click through to the SMART attributes.