DVD recorder hard drives can be tricky when they start to malfunction or otherwise behave badly. For most drives, the problem is actually related to fragmentation. The solution is often no more complicated than formatting/erasing the drive, using the built-in format/erase function of the recorder.
When the drive starts to "die", you may be out of luck.
Most DVD recorders use special proprietary formatting and partitioning on their drives. In some cases, there is special date located on the drive, something only the manufacturer could replace.
I've even seen special hard drives in use, where the hardware has been modified. This means you can't just go to the store, buy a new drive, and swap it out. Again, this is something only the manufacturer could replace.
Every now and then, for some models of recorders, some gearhead has experimented and found a way to replace a drive. (And many have tried and failed!)
I'm not personally familiar with this machine, nor do I recall ever seeing information on its repair (or its hacking). My advice is to look at avsforum.com, myce.com and videohelp.com, in their DVD recorder forums. Search their forums. I don't think you'll locate anything, but that's where I would search. Beyond those three sites, I don't think you'll find much else for DVD recorder repair/hacking.
Quick links for you:
http://club.myce.com/f89/
http://forum.videohelp.com/dvd-recorders-f28.html
http://www.avsforum.com/avs-vb/forumdisplay.php?f=106