its going somewhere, so you will have to put car on ramps, and you will need to have a good look around all seals and pipes, use a torch if nessesary. if all ok take car off ramps and check all around rockerbox gasket,if still nothing, start car to see if any black smoke coming out of exhaust, if yes, then it could be your rings are failing, if still nothing then it could be head gasket. if you take your car for a good run to really warm it up. park car and place paper or cardboard underneath engine and see if any oil drips down this sometimes gives you a clue if you do have a leak somewhere. happy hunting.
hope it helps, August 2010