Ok, found a work around on this one. Turns out I had to format the new drive first through the Set Up GUI for the terra station. Go in to DRIVES, select the drive and click format. This is a little convoluted since once formatted the raid array wouldn't use it, but the error 30 went away and the TS3400 recognized the drive as not being in a failed state. To get it back in the array I had to dismount it then remount (Scan Disk), again through the Set Up GUI. Once remounted is showed as unformatted again but not error 30'd. I went back into the RAID setup, selected the now unformatted drive, and did a Recover Array. It rebuilt the Array and now all is well.
Hope this helps someone else.