I've just noticed my 2012 Mac Pro has a bead of white silicon along the edge of the heat sink. Correct me if i'm wrong - I'm thinking Apple has added this as a tamper indicator. Alternatively, could possibly be to stop arcing of components and heat sink in that area? Has anybody seen this before? Is it on 2010 models? Anyone with a 2012 have similar sealing of the heat sink? Nanofrog - It was said in a previous thread of mine that the retention mechanism on the 2009 board is different to that of a 2010/2012 board Lidless V Heat spreaders. My board (most definitely from a 2012 machine), has a marking '2009' on the right side of the image. Any significance?