My parents just threw a party and someone brought a 5 gal Sanke keg of Lefthand Sawtooth. (Had I known it was going to be one of those parties, I would have brought a keg of my own!) Anyway, the stupid hand pump rented from the liquor store decided to stop working so I took it apart unfolded the wound up o-ring on the plunger and lubed it up with some olive oil! The thing worked like a charm and for the rest of the night I was the genius who made the beer work.
So the moral of the story is: olive oil works in a pinch. Not sure what it would do to the inside seals of a keg, or beer flavor.