The nipple on the side of the oil filler tube... yeah I've read the threads about the snot and the filter mod and the PCV mod and the catch can mod and all that, but what I'd like to know: If left open to atmosphere, is this considered a vacuum leak ? ( I'm to lazy to put a suck meter on it at this moment )

 

No, but it will allow the combustion gasses that bypass the seals into the crankcase to be vented into the atmosphere.

 

I put a pcv filter on mine. Sometimes it makes cool noises...