Hello. I just bought a used retina 13 from eBay. The keyboard is weird in the fact that half of it has the backlight a bit lower and it sound weird when typing. I opened up a couple of keys and found the everything in working order but the key caps where a bit dirty as in the pictures. Is there any other reason for them being like that other than liquid damage (coke or coffee by the colour of it)? Can this be fixed by myself? I cleaned all the affected keys and their clips but nothing changed other the the travel being smoother of the affected keys.