89 sentra, oil spraying all over engine

[accentauto]

i have a customer that has an 89 nissan sentra. he had it towed to me a few weeks ago. he was going down the interstate and saw smoke. he pulled over and there was oil covering the engine. after cleaning the engine i found no holes or any leaks whatsoever,. this car is immaculate!!! the only thing i found wrong with the car was a faulty pcv valve. after replacing it, and steam cleaning the engine, he picked it up.He has been driving it for the past 3 weeks and the same thing happened again. a few days ago. neither of us an find where the oil is coming from,n nor what is causing it. any ideas wold be greatly appreciated
jay(accent auto)