If Western Digital won't cover a replacement backup under warranty, here's my suggestion:
Very recently, my main hard drive on my imac was dying and had multiple bad sectors so it was difficult to back up using any traditional backup utilities because they would either time out or quit due to a read error. After a lot of searching, I finally found a solution using linux. It's a little involved for a first-timer, but I made a perfect backup of my hard drive and was able to restore 99% of my data, with only a few corrupted files that I cared about (pictures).
First, you'll need to boot Linux on your mac. Google how to get that going. I ran Linux Mint, but just about any current distro will be able to do the job for you.
Second, you'll need to run the dd command to copy the entire hd contents from one hd to another. This link will get you started, but there is certainly more than one way to do this. Google is your friend on making sure you run the correct command line so you don't accidentally overwrite your data. Note, I ran the "dd" command and it worked fine but took hours. Apparently there's a faster "cat" command which I read about here: http://unix.stackexchange.com/questions/144172/full-dd-copy-from-hdd-to-hdd/144227
Third, if this is too complicated/involved for your liking, take the hd to a computer repair shop and they will certainly be able to help you out.