I have an older iMac that I got from a friend and I want to factory reset it before I start using it. It has Mountain Lion and I've read the procedure for factory resetting but I have concerns about reinstalling the OS. Basically, I'm afraid if I wipe the computer and then get to the point where I have to download ML again and it doesn't work that I will have a bricked machine. How can I tell if the OS will download again without licensing issues, etc? Thanks.