Hi mate,

Just reading about your problem, Ive known this to happen when the original breather non return valve fails on the manifold, allowing the crankcase to pass oil into the manifold causing a smokey exhaust on the overun when manifold vacuum is high. As you have an uprated breather system this unlikely to be the cause of your problem

Going on what you are saying I cant see it being stem seals causing oil in the inlet but it may be causing your smoke on overun as this would draw oil straight down the valves and into the combustion chambers. For oil to transfer this way to the manifold it would have to run uphill, somewhat unlikely. Are you sure it is oil in the manifold and not a build up of sludgey carbon?

A good way to check valve stem seals is to leave the car overnight and see if it smokey on start up in the morning.

Let us know how you get on.

CheeRS, Mike