Hey there, SLoth_1.
So you want to use it simply as a secondary storage drive in a non RAID configuration? You shouldn't have any problems with that if this is the case. What old files are you talking about, when one of the drives in a RAID 0 setup fails, unfortunately all the data is lost, so you could simply reformat the other HDD/s if you don't want to use them in a RAID, or simply try to setup the RAID array from scratch and start writing new information to see if you'll have the same problems.
You could also try that drive with a different SATA port and different cables, to see if the issues still persist. Downloading its manufacturer's diagnostic tool to test it, just to make sure that it's OK would be a good approach as well.
Hope that helps. Please let me know how everything goes.
Boogieman_WD