I had a Mid-2009 Unibody MacBook Pro 13" which started to freeze and at some time finally refused to boot any longer, the CD-Slot didn't work as well. It worked by booting from an external USB drive, so I assumed the SATA-Controller was toasted. I went to an Apple Store, told them that and the "Genius" said that no way it could be the SATA-Controller, it must be something else, propably the HDD.
He went into the back of the store and examined the MB, came back displeased and told me that the SATA-Controller really was broken. Then he smiled and told me that one of the indicators was somewhat brown (not even completely), so he refused to repair it under the AppleCare warranty I had bought. I should have paid something like 600, or about half the price the Mac cost without extra warranty.
All indicators had some light traces of corrosion, but it didn't look like they became colored because of water or something.
I got my new Retina MacBook Pro 13" delivered with 10 white pixels/pixel groups, a unevenly typable keyboard and a broken trackpad which only works properly in the bottom right quarter, everywhere else you have to press much harder and the bottom left edge sometimes remains deep down with a loud cracking noise after clicking it.
The mainstream-massproduction-products Apple makes now aren't of the same quality as they were some years back.