if there's a MOB issue, like a loose solder point or component of poor quality, the intermittent functionality of the keyboard is probably due to its orientation so closely over the "hypothetical" problem coupled with the nature of a keyboard - basically a repetitively tapped/pressed sheet.
and on a side note, ripbox, I purchased a Sony vaio for $249 at BB, it was one of those models that had some type issues and they quickly abandoned! Well, nearly 6 years later, plenty of abuse, even being completely submerged while on in tap water, it is one of my favorite computers! You weren't saying anything bad about them or anything, I just thought it was pertinent, they (at least can be) a great machine.
i guess it could technically just as easily be a corroded connector pin to the keyboard ribbon line, or the likes. but if ripbox has had a lot of experience with similar vaio keyboards and found it to be the MOB, I'd bet on the experience.