If the bad sector was in unused space then the new disk should be just fine. Which is likely, considering that only 1% of the virgin drive is used. However, if the new drive has a hole in it, not the old one, then when Tivo gets to it eventually - it will result in error or lost data. So checking the drive with WD tool seems like a very good idea. Another, albeit crude, way to check if the source drive is bad is to do "dd" copy to "/dev/null". If there is a an error it could only come from the source drive.