Are Oil Free Air Compressors REALLY Oil Free?

Theres different types of "oil free" compresssors. Some are just sealed units like SS was saying and others use sleeves/teflon coatings and completely do away with oil. The sealed unit would have to come apart to the point the factory put the oil in then sealed back up but would need to know if the oil just came out of the intake/exhaust or if theres a crack.

Ive worked with several high end types for medical applications.