I would just do a smoke test before pulling things apart again.
You can rent these machines or just get a cigar and good bottle of booze and do that way.
Remove air tube from intake, put food wrap or ?? over intake hole and tape it up to seal it.
Remove vacuum hose from PCV valve for adding the smoke to intake.
You use PCV Valve hose because that valve will be closed when there is vacuum but wide open if there is pressure, blowing smoke into intake is pressure, and most of the smoke would go to that hose.
Light cigar have a drink and start blowing smoke into the PCV hose and intake.
The intake is sealed pretty well, most air flow will go to open intake valves and passed the rings, but if there is a leak that will allow air to exit as well and with it some smoke, so keep an eye out.
Sometimes takes 1/2 to 3/4 of a bottle to find a leak, these things take time, lol.
I think you asked about the PCV valve on another forum, have a look here: Positive Crankcase Ventilation (PCV)
PCV Valve is pulled closed by high vacuum, like at idle or deceleration, so restricts vacuum going to valve cover.
As you accelerate engine vacuum goes down and PCV valve open more.
So there is always some vacuum in the valve cover/crankcase areas but never 18", always lower vacuum, just enough to maintain positive pressure that will pull oil vapors into the engine to be burned.
PCV = Positive crankcase ventilation.
positive in this case means there will always be a little negative pressure in the crankcase......when engine is running.
Marginal air leaks can show up on only 1 bank.
Lean code is not what most think it is.
Lean code comes from the length of time the fuel injectors are open.
If the computer thinks it is having to open the fuel injectors on one bank longer that it should then it will set the Lean code.
It is quite normal for fuel injectors to drip a bit when they get dirty, so spray but a little drips, this would cause computer to open these injector longer, not enough for lean code, just a little longer.
Now say you have a small vacuum leak, not enough to effect performance but extra air is coming in, by passing the MAF sensor, so computer has to open injectors a little longer.
When the two things are combined..................Lean code on 1 bank, maybe other banks injectors are cleaner, or may be leak is bias to one bank more that the other.
Point is there is a line drawn as far as injectors open time, if the line is crossed then Lean code, if other bank is at the line but hasn't crossed it then no Lean code.