One old piece of advice from one old techie type person... not a Mac expert, but the advice mostly still holds.

If you have a suspected flaky disk, NEVER add a 'fix it tool' (or ANY new disk writes) to that drive - you may trash info by overwrioting things, dir entries especially. If you have only one physical disk, you are in trouble, unless you already have the tool loaded - but of course it may be corrupted too............

If you have 2 or more disks, even installing the tool is still risky. If the flaky disk has an OS (any) on it, then the OS will probably write some info concerning (maybe even just links to) the newly installed appln, still trashing direstory entries on the flaky disk.