WD40 in the headphone jack...ahhh.. that's not a bad idea.. in a way. I wouldn't use WD40 myself. Toothpick to start.
I remember reading about a problem with the jack. When the headphones are in the plug pushes a ring? in the hole that tells the system to output sound thru the jack as opposed to speakers. Once in a while, upon removal of the headphone plug, the ring would not disengage. Guys were reporting success with diddling around in there with a toothpick till it released. But that doesn't sound like your problem. Have you been using headphones lately?