So before I saw you a picture of CrystalDiskInfo to tell me what's going on, I would like to start with something first. So I bought a WD Black 6TB like 1-2 months ago and when I scanned it for problems, it had reached maximum reallocated sectors before me even getting a file one it. So I RMAed it, got another one (the one that I have now) and has reallocated sectors again. My guess is that when your RMA they give your refurbished that is already returned for probably the same reason as mine (if they can partially fix this themselves).
Here is the pic: http://imgur.com/a/HOjBj
Here is the pic: http://imgur.com/a/HOjBj