DIY Disclaimer: I hold no responsibility should anything goes wrong when you decided to follow my guide. It’s strictly meant as a reference for knowledge sharing purposes.
Symptom:
We can smell oil fume from inside the cabin through the a/c vents but it stops when we switch to internal air circulation mode.
From the engine, you will notice the valve cover is wet with oil stain as follows
A check on the parts catalogue revealed that this N46 engine belongs the the LCI model with 156hp, some called it N46N as my E90 320i was the last batch of the pre-LCI model. There is no more CCV in my model
Below is the part catalogue for my vehicle where this membrane is missing:
Part Code: 11127555212
Online search pointed me to this website where they actually make the repair kit: http://vanos-bmw.com/membrane-for-cover-n46n-bmw-11127555212
I then contacted the local parts dealers and found out they do not sell the repair kit, but the entire valve cover.
Running out of option, I attempted to pry it off and see where it takes me..
After one hour of careful prying.. VIOLA!!
You will notice centre of the membrane has detached from the rest of the section, hence allowing oil fume to escape.
Carefully, I cleaned them up, took out my cobbler glue and used bicycle tube (refer to the black color item below, shaped like a flower 
).
Then I put them together.. to reinforce the broken centre piece.
Mission accomplished!
I assemble the kit and cap it back in. One mistake, I forgot to reattach the spring.. 
Another round of prying to refit the spring.
Thank you for reading and please provide feedback or query if any.. 
Updated: 11/4/2016..
It has been working fine now. 6 months down the road..
Ta-dah! No more oil stains, only dust stain. The leak was actually very serious, I lose lots of engine oil.. so mush so, it drips on my porch. Now my porch is dry like a dessert.. ! I’m pretty sure if I were to visit a mechanic then, they will most likely advise to replace flywheel oil seal and oil pan gasket. Pheew!
To all N46N owner out there, please take note!
