Is my hard drive dying?

I keep all my data on a Samsung hard disk drive. Recently when I tried to make my regular Macrium backup it failed with an error message indicating that there was a problem with the disk. I ran Crystaldisk which failed it and found 4 pending sectors. I then tried the Seagate disk tools (since Samsung hard drives have been taken over by Seagate since I bought mine) and got an error message saying disk fail, request replacement. However, it also suggested trying to zero-write the disk before returning in case that overwrote the bad sectors identified.

I've low level reformatted the disk a couple of times and wrritten zeros to the whole disk. Now neither Crystaldisk or Seagate tools can find anything wrong with the disk, and the low level formatting software I used found no bad sectors.

So is my disk fixed, or is it an expensive paperweight that's waiting to fail? For what it's worth, it's nearly three years old. WHen I bought it it came with a three year warrenty but Seagate doesn't seem to think it's covered by them any more. So despite being under warrenty I won't be able to replace it - especially if I've just gone and done something to it that has eliminated the bad sectors and made it look good again!

Incidentally as soon as I first got the Macrium message I swapped it for a good disk, so I haven't lost any data. But it would be nice to know if I should continue using it for non-intense things like non-critical data backups or not.

Look at the label on the drive for a date, could be it was on a store shelf for awhile before you got it. Sometimes products don't get to the seller right away. If you have the sales slip/invoice from a reputable dealer Seagate should honor it or maybe you could return it to the seller you got it from. If the drive was handled like some cameras are with the Gray Market, it may not have a legitimate entry into the country.