When HDSP says the drive's health is at 14 PERCENT, it is a goner. The overview tab is likely all red (I see a red X at the top) and says backup your stuff now, the ship is sinking... Replacement is now non-negotiable.
As far as installing a new one, it should just be 4 screws (either bottom of drive or on the sides with brackets) and 2 connectors. That's all there is to it. If the recorder has a model sticker anywhere, or if you can also post a pic of the front panel, that would be helpful. Or even a pic of the client software you use. Those are all viable clues.
I'm not sure as to the specifics of what HDSP determines to be bad sectors vs reallocated, but as
@alastairstevenson said, each drive is shipped with a stash of "spare sectors". When the heads come across a bad sector, it flags it as unusable in its internal sector map, so as the drive moves on it knows never to write to that area of the platter(s) again. After so many sectors fail and it runs out of places to reallocate the data, or spare sectors (different areas of the platter) that is when SMART generally is going to report bad sectors. Reallocated effectively is saying that's how many died, but were replaced with good ones so you should still be fine. However, as that number continues to rise, it's a sign that there may not be an end in sight and replacement could near as it is quickly depleting spares.
Hard drives are very much sensitive devices, both physically and logically, which is why SMART and
tools like Hard Disk Sentinel are priceless, especially when a drive contains important data such as incriminating evidence or a decade's worth of family photos. Hard Disk Sentinel is not the only diagnostic application to make these determinations, but I have found it to be extremely thorough and powerful insight into what's going on with a given drive. So I've just stuck with it. I see it has also helped you make the determination that you unfortunately need to purchase a new drive :/
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