Here's a screenshot right from the N54 engine mechanics PDF in the sticky:
Not sure if its the drawing BUT take a look at where 1 is indicated. It's actually right before the elbow tube that has a pipe on it that goes to the rear intake pipe. So it seems that the checkvalve is actually NOT what we think it is even though I looked at that piece yesterday and there definitely was a checkvalve right in there...wtf, I'm confused now...is the checkvalve in the elbow part that sits on top of this outlet (which is what I think it is) or is it before the elbow piece???
1 & 3 is for the two checkvalves..they both seem to be right next to each other..."1" is the one that shoots out air with oil vapours into the rear intake pipe (or the OCC/breather if you're running it)...this happens under boost...
where does "3" come into play (the other checkvalve)??