Is there any risk for the private data to send my faulty passbook to WD for replacement?

No.  When a drive comes in for replacement, it’s removed from the case and immediately stuck into a machine that both checks the drive status and wipes the data completely and irretrievably.  No one can view the data, or recover it when it goes into the machine. 

Thank you, Bill. That is really helpful. Stone.

You are welcome.