I purchased my 2013 27" 2.9GHz i5 iMac when it first was available to pre order, at the time i could only afford the model with 8gb of memory. I now am looking to add more memory (ideally another 8gb) but rather than aftermarket i want to use the genuine apple memory exactly the same as what is installed in the machine already. Does anyone know where the best place to get the memory from at a good price? Perhaps someone here has removed the 2 x 4gb ram to replace with larger and is willing to sell? Any info or help is appreciated.