I am not sure how to play this one !

My 3 month old MacBook Air is going in to the genius bar tomorrow.

I was using it the other day, then I had a swig of coffee .... Next thing I know there are two small droplets of coffee on the Palm rest - not sure how it happened ! Now I am usually very careful to avoid such things and reacted lightening fast with a piece of tissue - I was 100% sure (at the time !) that no coffee had found its way onto any keys.
Then the following day ... My comma and full stop keys have stopped responding

Now I know you are thinking "idiot -it's obvious what has happened". But I am not so sure ! Honestly I am convinced no coffee went inside the machine . And I certainly can't see any when I gently prise up the affected keys (surely if even a tiny drop had got in there would be some discolouration from black coffee ? ) the keys are backlit so it should stick out like a sore thumb.

Bizarre as it sounds , I am convinced this must just be a coincidence !

So my question !

Should I simply say nothing - just say the buttons stopped working ? OR Do I tell them the whole truth? Id hate to get one of these fabled helpful genuises that might have bent the rules a bit for me , only to piss him off having him think I'm trying to pull the wool over his eyes.
but then on the other hand I don't want to admit to liquid damage if that not what it is ! We really were talking a tiny amount of coffee , literally about a quarter of a raindrop in total ! If that has cause a problem then I am not really impressed as I have known lesser laptops survive immeasurably worse dousings !!