Quick question: I'm looking at purchasing a new bottom case for my 2010 MBP. I'm curious though, what's the difference between the 2009-2012 (A1286) bottom cases? Theoretically, they should all be identical. Although, I'm noticing a somewhat shocking difference in price between them. For example: 2010 bottom case: 2011 bottom case: Notice the difference in shielding/insulation plastic on the underside?