it could be lifters, rocker arms, valve springs who knows. no oil causes a lot of problems. either way the only real way to find out is to pull the engine apart.
buy some dye (prefferably green) pour it into your power steering system and use a black light to find the leak. Thats one way of doing it. Most of the time the leak occurs on one of the power steering lines where the metal turns into rubber or vise versa.