I have the chance to buy a mid 2008 MacBook Pro 17" 2.5Ghz for around $550. It has the Nvidia 8600M GT card which so far apparently has not given any problems to the previous owner. Am I taking a gamble? According to the serial number the laptop was manufactured in July 2008. When is the cut off point for having the card replaced if I am unfortunate for it to go. Any advice would be appreciated.