I recently sent a HD to Seagate. The packing instructions for a Seagate HD are here.
http://www.seagate.com/ww/v/index.js...001a48090aRCRD
The WD instructions should be identical.
If you do an Advance Replacement, and they find nothing wrong with your old HD, they may charge you for the replacement HD, since they have your credit card info.