Because the drive is set up with a non standard file system, the only way I can think of using a cradle to clone the drive to a new 2.5″ drive other than a roundabout route using a digital modulator and Freeview-HD PVR to record the recordings in real time. Watch the recordings using the Freeview-HD pvr.
Possible problems is that you are likely to clone the faulty sectors so finishing up with the same issues.
Or if you fit a larger HDD the box might not be able to use the extra space.