Backup systempartition to eSata-drive
I had one of those same drives and could never get it to work with an ESATA connection. When I called WD about it they said that model does not really support ESATA connection. Moreover, they said they knew about the problem and were not going to fix it.
So what I did was use FireWire instead - that worked A-OK. Later on I got a WD 2TB USB3 Passport "pocket drive" (much smaller, no power connection, roughly same speed as Fire Wire) and took the original MyBook apart and put it's drive in my PC case where it works fine as an internal SATA 2 drive.