Use the WDC software to diagnose your HDD, if the result is fail then you may proceed with the RMA, if your shop still able to process your RMA without extra cost then you may just send there, save some $, if not you may choose to let them earn a bit by packing and sending for you or you may try to send it yourself over to WDC in Malaysia, I have yet to send a WDC one, found the RMA process in the web is slightly tedious than Seagate.

There're several diagnose methods, did you tried them all?
If all diagnose returns OK, then you may disk wipe (Low level format tool) to try to rectify the "Pending Sectors Count", it can solve by re-writing and reading the sectors again to verify if it's still OK, otherwise it'll mark as bad and you'll see "Reallocated Sectors Count" raised.
Before you do this, backup all the data on the HDD to another if you have enough space, otherwise borrow friend's external HDD for few days .
LLF (Low level format) tool can be obtain here:
http://hddguru.com/software/HDD-LLF-Low-Level-Format-Tool/
Use the free version which will cap your speed at 50MB/s, will take quite sometimes if your HDD is huge.
Or you might be able to find similar function at WDC diagnostic tools (WRITE ZERO).

If you are comfortable with using the 'cmd.exe', Windows also provides a built-in command line utility 'diskpart' that will allow you to write zeros to a HDD. Be careful with this utility, as you may accidentally wipe the wrong HDD if you made a mistake.

It should be as simple as:

1. cmd (Run as administrator)
   
2. diskpart
   
3. list disk
   
4. select disk 0 (Replace the number with the disk's number that you want.)
   
5. list disk (Double check that you have selected correctly.)
   
6. clean all (Warning! This command will write zeros to the entire selected disk, destroying all data.)
   
7. exit
   
8. exit
   

Asides from 'diskpart', there are also other free tools like 'CCleaner' that writes zeros throughout the entire disk. Regardless of the tool that you use, it should take roughly 3 hours for every TB on HDDs. You can get a better estimate by taking your HDD's capacity (in MB) and divide it by your HDD's average write benchmark (MB/s). Any tool that does significantly faster, like shortly after starting or half the expected time, either didn't do a proper job or you estimated the time required wrongly. Unfortunately, 'diskpart' doesn't have a progress indicator.

Do note that wiping a HDD by writing zeros makes data recovery on the HDD impossible. It is a good idea to wipe a HDD or SSD by writing zeros before selling, RMA, or retiring it.

Perhaps a little bit on the expensive route but I suggest getting the SSD drives for your notebook and desktop boot drive. Don't need to get bleeding edge SSD. Just a normal bang for the buck one will do wonders for speed.

Then go for external drives or invest in NAS for large storage. If you have a few PCs / notebooks connected via your home network, best would be a NAS. Nowadays Seagate and WD drives should be fine. I hear Toshiba drives are also excellent. If you can get Hitachi, that would be best but hard to come by.

Spindle speed? 7200rpm for performance and for home use storage, best to get 5400rpm to keep heat and electricity bills down.
Yeah, my 6TB WD Red drives also damn expensive at the moment. Blame it on the weak currency. 
How old is the drive? If there's already warning, best is to get ready and transfer / backup your data. It's not like a car where problems can be repaired.