A couple of things before you go that route.

If it is not just the drive that has become faulty you will end up with a TiVo that is no longer covered by warranty.

The TiVo reports it's drive details as part of the daily call, so if you connect with a replaced drive you do run the risk of not getting any assistance from them for the other hardware issues.

Hybrid do not repair your TiVo, they exchange it for another one. From the reports I have seen, the replacements have all appeared to be new units (the refurbs are sold on eBay via premium home theatre).

WinMFS is designed to be used to copy a TiVo Drive to a larger replacement drive. As long as there is no non recoverable corruption on your drive it will work.

Peter.