I have been looking at getting a new 2012 iMac on ebay but now after reading about all of the horror stories related to the various screen issues I am thinking otherwise. Screen issues such as grey patches, dust, grey clouds like watermarks. Is it worth getting the new iMac over the old to guarantee that these sort of problems won't be present? I am a heavy user so I*will be punishing the mac doing all night rendering sessions at times for my masters work. Other than that it will be on every day so I don't know if the 2012 will be up for that given the screen is insulated between various layers of glass and plastic which don't let the LCD cool down under continued use. Any help from old and potential new users should clear things up. Thanks in advance.