Need to down load a copy of mountain lion 10.8.3, an redo my Mac book. Have major issue with Apple Mail an the Apple geniuses could not fix it. But they used the information on the computer to let me do a repair install. I think I can download any version an put it on the Mac, does not mater if its a MacBook or iMac, am I correct? Is it possible to get a copy off of the App Store with out ponying up $20?