Based on what I saw on Ifixit's teardown of DSi/XL and even the 3DS, it seems that these handhelds are not using the same kind of trigger switch found on the GBA family and DS phat and lite due to the appearance of the triggers. My guess is the trigger switch of DSi looks like the buttons of a mobile phone keypad which the metal discs of the buttons are being held by some sort of adhesive coating. I'm think that the way of cleaning the metal contacts might be similar on the OP. Sigh... I never tore a DSi down yet.