I just replaced a WD Black 640 3 years into its life. Blacks have a 5 year so they RMA'd it and sent me a 750 in its place.
I do however have a Seagate drive laying around somewhere that has almost 10 years on it and it still functions flawlessly. But it is admittedly smaller given its age and that may contribute to lifespan. Either that or Seagate has slipped in the last decade.
Seagate apparently has slipped in the last 2-3 years. (Could this be related to the hard disk shortage due to flooding in Malaysia?)
Hard drive failures tend to happen more for drives that are power cycled a lot, and for drives that undergo big swings in temperature (even when the temps are all within the rated temp range).
I do however have a Seagate drive laying around somewhere that has almost 10 years on it and it still functions flawlessly. But it is admittedly smaller given its age and that may contribute to lifespan. Either that or Seagate has slipped in the last decade.