Hokay - Ive ordered an SG Motorsports AOS for the Gen V. Call it a pre-emptive strike but in the fiddling around with the IC to TB hose (new silicone AVO item last installed), I was conscious of some oil in the pipe and IC, enough to wet the surfaces and form drops in places.
Cant be good for efficiency, octane rating or carbon buildup in the engine. car has 70K km on it, so not esp old!
So thanks BBB for the info in this here thread. Having done some Googling for Gen V fitment, there's not much out there, though it should all be pretty much same as MY15 WRX given the low mount twin scroll turbo set up, as well as the fact that the IC/manifold set up appears to be the same.
So I'm thinking the install should be pretty straight-forward: AOS goes on the Oil filler, after first clocking the two parts to ensure hole alignment and pipe in/out orientation.
Intercept head-breather crossover pipe, route to AOS, then reconnect back to crossover pipe. This is assuming I can correctly identify these pipes after removing the IC...
No idea if I may need Y junctions etc?
I will also check the PCV valve is rattling normally and is free of any gummy residue - it will cop a clean out at the same time.
I'm working on the basis that the oil mist is only entering the pre-turbo intake pipe under boost/WOT when the crankcase is starting to be pressurized by blow-by, which will cause the PCV valve to shut and then forcing the blow-by out through the rocker cover breathers and into the pre-turbo intake pipe. With the AOS in place, the back-flowing oil mist/blow-by should deposit it's oil back into the filler, leaving mostly clean blow-by to return to the pre-turbo intake.
The rest of the time the PCV system should operate as normal, ie: fresh air drawn in from the pre-turbo intake pipe, (detouring via the AOS) then into the rocker-cover breathers, then air/blow-by out via the crankcase breather and CCV valve into the high vacuum area of the intake manifold.
I plan to take some pics and do a "how-to" as I go when time permits in the next couple of weeks.
Thoughts/discussion/correction of any of my delusions welcome