I was looking at the old red pipe a couple of days ago and noticed that it actuall reduces in size at the FMIC end. Also there is a metal lip inside that reduces it still further. It is certainly NOT a smooth pathway for air flow and from what I can tell the metal lip I mentioned seems to trap oil and that is where the oils seems to be forced through on the bottom seal.
I currently have no leaks but must say my car seems to have foud a new lease of life after getting 100 miles or so on it followingthe fitment. The response is noticably sharper in all gears and has more urgent feel about it when accelerating at all revs. I don;t think it atmospheric related as we are currently have some very hot days but my car is just totally manic right now and I'm loving it
Maybe the improved airflow required some adaptions by the ecu and it is all at a peak now