@Amiga4k
The thing is that physical and logical mapping don't match. If you say block x is broken, that x is by using the logical mapping. What happens is that 'block x' can actually be any block on the physical drive, and it can even change without the user knowing anything about it.
To my knowlege adding bad blocks with hdtoolbox only works for some really ancient SCSI hdds (ones that also support low level format). With these there is no automatic remap/data relocation of bad blocks, and the thing must be done manually.
There are tools that actually allocate the storage used by the bad blocks (they create a file that covers the damaged area). These were mostly useful with floppies though, as there the bad blocks don't move.
My argument is: If the drive is indicating any errors to OS using it, it's time to swap the drive. Even if you might be able to get it working for some months, you could just end up with catastrophic data loss later on. If the drive is acting up, copy the data to a new drive while you can (if you can). HDDs are dirt cheap these days, don't gamble with your data.
As a side-bar: I have some 1.3 TB of hard disks running 24/7. I've had one IDE 2.5" laptop drive die, and two SCSI-II HDDs.
