Regarding your WD external HDD:
SMART isn't showing any signs of problems or potential failure with the drive, that's good; by SMART itself, you probably won't have any issues with reformatting and re-using the HDD. However, the fact remains that you've experienced file system corruption resulting in data loss on this HDD, so I would recommend replacing with a new HDD if you have doubts about this HDD.
Overall: External HDD will probably function without issue once reformatted, but since the backups you've been taking on the drive appear to be crucial I advise replacing the drive at your earliest convenience if you have any doubts whatsoever about the drive.
Regarding your internal C: drive:
Now this is something you should be worried about; much moreso than your external HDD. SMART is showing that your HDD had to reallocate some sectors, this means that your HDD had trouble writing data into the sectors while the drive was in operation and had to remap and move data from the bad sectors into special redundant sectors specially reserved for cases like this.
This means one of two things:
A: Your HDD experienced a minor fluke while in operation and tagged the sectors as bad. While not required, problems of this kind can sometimes be fixed by reformatting or running some kind of disk scan on the drive.
B: Your HDD could be experiencing physical wear such as a degradation in the magnetic material coating the HDD platters. This is an actual physical problem with your HDD and your drive will eventually fail.
It's impossible to tell which of the two it is just from SMART, combined with the fact that the number of remapped sectors is low. However, SMART is showing one way or the other that your HDD is experiencing a problem that could eventually result in a complete failure of the drive.
I would backup your C: drive ASAP and then check regularly to see if the reallocated sector count keeps increasing. If it doesn't increase any further, I would think about possibly replacing the drive at your earliest convenience while taking routine backups on a more regular basis. If the reallocated sector count increases any further however, immediately replace the drive before it completely fails or you might experience data loss.
I'd say this was overall a good checkup. While we didn't find any apparent problems on your external HDD, we did find something to worry about on your internal C: drive. :shock: