I'm wondering which week build was the discolouration supposedly fixed. My Macbook is a week 31, and while it hasn't developed discolouration on the casing, the keys are going yellow and won't come clean. Also there are very slightly noticeable dots of yellow appearing in the top right hand side both inside, and out. the mains adaptor plug also has yellow on it. So i've switched it with the other one included. Laptop still works brilliantly, but i'm wondering can you clean something like this off?