Check your exhaust pipe for signs of oil (wetness or lots of wet soot buildup) and check your fuel, see if it looks like it has motor oil in it (makes it turn brown and swampy looking).
When the high pressure oil o-rings fail on the injectors the oil usually goes into the fuel.
You might also want to check the left rear of the engine near the top. The high pr oil manifold leaks there a lot, you may not see oil leaking on the ground near the engine as it likes to run down onto the transmission.