I'm keen to upgrade the SSD in my Retina - just wondering what the options are? I know it needs to be either the OWC or the original Apple unit - just wondering where I should by from? I've been looking around and they are very well priced from iFixit, but they never have stock (I assume they only get when they buy an MBP and strip it down for parts). Also seen them on eBay, but often the sellers look a bit dodgy. Anywhere else I can look for them?