Have you tried taking the drives out of the RAID config, ghosting the image, and then secure erase them?
I have been running two X25-E's in Raid 0 for almost as long as you have. Every 3 months or so, I pull them out of the array and run HDDerase 3.3 across both of them. In every case, this has returned their throughput capability to their former glory ie... VERY VERY FAST!!!!