So I did change the string and put the firmware back on the camera, rebooted and I was able to log in via telnet and web interface. Alas, the web interface is now Chinese only, before applying the patch it was multi lingual. Guess I have to look into the next issue: finding and applying an...
I too would be very interested in the search string for 5.1.6 as well. My new DS-2CD2032-I came with 5.1.6 pre-installed and my servers NFS share mount on the camera is only maintained for a few minutes and then the state goes back to 'un-formatted'.