I have done almost same way but it’s not working…I have created similar disk partitions (8 partitions) with modified debrick script from this instruction: http://community.wd.com/t5/My-Book-Live/GUIDE-How-to-unbrick-a-totally-dead-MBL/m-p/435724 and using rootfs.img from latest firmware but no success.
Only difference I just noted is that I’m connecting via USB-SATA. Maybe that is causing problems?
