First go to the GIMP Plugin Registry at http://registry.gimp.org/node/16231, download a file called "rotatebrush.scm".
Then use the terminal to sudo into your file manager. Type sudo and the file manager name. Mine was "sudo thunar" Yeah, it's password protected. Type in your password, hit enter. Congrats, you have just used the command line. Not scary huh!
In the home folder goto the GIMP 2.6 folder. It's a hidden folder, goto View and check hidden folders if you can't see it.
Close the windows and open the GIMP.