I am planning to buy a new iMac soon and will be selling my existing one. That one is mid-2010 and came with Snow Leopard. I have since upgraded to Lion and then Mountain Lion through the App Store. Should I clean install and just put Snow Leopard on it? Or can I put Mountain Lion back on? If I put Mountain Lion on it, will it leave some sort of connection to my Apple ID? Which would you do, or have done? Thanks!