Yes, as you have read… it is perfectly possible to reinstall Disk Utility.
My primary partition on my MacBook 2,1 runs on Lion (and i'm using it right now). I have an extra partition in which i've manage to install El Capitan (and it goes fine), but as Migration Assistant doesn't work… the computer went to sleep during installation, so the creation of a new user was required in order to complete the process.
By trying to do a manual transfer (to El Capitan) of system preferences/desktop configuration/applications fixed in the dock/other stuff… original user (from Lion) was screwed around. I had to manually copy everything by changing permissions from El Capitan… it's fine now or half fine, as Lion loses some configuration on start up.
What does have to do with Disk Utility, well it's required for restore permissions. As part of the same issue, it was not possible to activate Debug mode (to see hidden partitions) from the Terminal. So, as when Safari stops working… i just used Safari.pkg for reinstall it. In this case, for Disk Utility, there's no Disk Utiliy.pkg so i searched for a MacOS Lion 7.5 update.
Using Pacifist, searched through mounted .dmg and find Disk Utility.app, but instead of using "update"… i just pressed "replace", assuming that this will be a "fresh install". Well, it wasn't, data from .dmg was incomplete and Disk Utility stop working. Checking console showed me a missing ".nib", looking directly to the contents of the .app… well, there was a lot of files missing.
So, here's the trick...
- Get the original OS X Lion Installer 7.0 (yes .0) in .dmg format.
- Delete Disk Utility.app from Utilities Folder and empty the Trash.
- Open the OS X Lion Installer with Pacifist.
- Navigate to Disk Utility.app (this one include most of the files that required) and chose "Install to the original folder".
- Close Installer window and open OS X Lion Update 7.5 again with Pacifist.
- Navigate to Disk Utility.app (which contains the rest of files that complete the application) and chose "Install to the original folder".
- This time the key is to press "Replace" when required (to preserve the previous installed files).
- Close OS X Lion Update 7.5 window and exit Pacifist.
The only thing that it's still not working it's that by forcing Finder to restart, settings are lost. I can't manage to restore the right permissions that will allow the preferences to save themselves.
I hope that this little guide could be useful for anybody else not being able to use Disk Utility.