On extracting the disk from its' external USB-connectable case:
[be prepared to lose warranty as a possibility]
my experience with both wd's and toshibas is that the lid will unclick with a bit of consistent care (as the youtube links in this thread show). Although I've not come across this yet, I have read that in its' more recent models, WD has fused the small logic board to the SATA socket, presumably to prevent successful extraction. Prices on the "external" encased disks are up to 20% less than the SATA-only ones. Why encasing the SATA disk for external connection should then cost significantly less than the SATA disk by itself remains a marketing mystery.
Seagate external USB-connectable "thin" disks (up to 2TB) have the "lid" glued in with double-side tape - at least the two I've disembowelled did. To soften the tape glue to prise the lid off, I resorted to warming it first along the edges with a hair dryer. Worked ok.
Mostly the USB-connecting logic board has failed, but the SATA disks themselves were reusable in another cheap external case - one that reopens easily. So far, only one disk itself was unsalvageable.