Pull air box off open throttle body butterflies and look down in there. see a bunch of oil, you have your answer

 

If you are losing oil, but it isn't showing up on the outside of the engine... it's gotta be going somewhere. Going to be either rings, or plenum. You can look down the throttle bores, and see if you can see oil pooling in there..... (if you can, it's REALLY bad...) Or, pull the throttle body, and use a small mirror to look at the back of the intake, and see if there is oil. (better test)

if the plenum is ok, next step is dry/wet compression test. If the numbers jump on the wet test, rings are bad.