Nissan Repair: Intake manifold, intake ports, manifold valve

Question
Valve cover is leaking oil on a 85 300zx tubro.
I disconnect hoses and electrical connectors and then remove intake mainfold collector cover and collector with throttle chamber. The intake ports are oil dirty, but one not. it's clean and think a cylinder or piston not firing or something else,could you help me on this.
Thank you  

Answer
Ken,

My bet would be that the injecor is not working on that cylinder.  But, before you replace the injector I would do an ohms check on it and compare it to the others.  Also, I would do a compression check on the engine after you put it back together.