Back for Help Again. Boost leak. A2A

turtle64b

Hey guys, instead of modifying my original help post (I seem to be posting these a lot lately ...), I wanted to avoid confusion regarding symptoms. I appreciate any input you have. Here goes:

Symptoms:
Pressure fluctuations throughout the RPM range, worsening as pressure rises
Saw a max of ~9.4psi @ ~7k RPM (at least consistently > 8.2psi) with the 8psi pulley in Oct of last year
Now can only achieve a spike of ~8.7psi @ ~7k RPM with the 9lb pulley, but never consistently (consistently ~8psi)
All pressures read consistent between my MAP sensor and independent boost meter (2 separate tap points, both off intake manifold)
The block off plate where the a2w intercooler used to be develops a small leak around 15psi (not too worried about that guy)
5/8 breather vents a significant amount of air when manifold pressurized and 3/8 PCV line connected to manifold. Vents much less air when 3/8 PCV line disconnected and capped.
Oil filler cap vents pressure when manifold pressurized. Missing O-ring. Obtaining new one and replacing.
The car is 100% daily drive-able right now.
No intake piping leaks from charge pipe entry to the throttle bodies.
No leaks from any vacuum lines for boost meter, fuel regulator, BOV, or brake booster.
No leak at the MAP sensor port or from the MAFs.
AFRs, fuel trims, everything else on target for data for tuning

What I've done:
Pressure test literally every joint in the intake piping to ~20psi except the SC outlet coupling (I don't think I can reasonably test this joint...)
Disconnected 3/8 PCV line from the manifold and capped. This led to excessive leakage past oil filler cap after driving for tune data.
Pressure test revealed small leak at a coupler from the intake Y to a TB. Fixed.
Switched to a full speed density tune to fix the lean issues. HOWEVER, this would also mask a pressure/vacuum leak, I think, based on how the SD tune works.

Thoughts:
Maybe a leak at the one place I cannot pressure test - the SC outlet. But 2 psi there?! I think I would feel that...
I feel like something is wrong in the sense that I can pressurize the manifold and get pressure venting from the crankcase/valve covers/oil filler cap. Since the system slowly bleeds pressure, would this mean that a constant pressure source (SC) is keeping the aforementioned areas under pressure? And I'm pretty sure this is bad, although I admit naivety in this area of engine mechanics...
Belt slip due to going to the smaller 9lb pulley? But silent? I had some slippage on the SC side that squealed a little, but a tightening solved that. I can't hear any other indications of slippage... BUT that would explain the loss of pressure up top.
Lastly, something internal post-intake manifold? Honestly, and hopefully not, this is about the last place I can think to look for a problem...

Again, I appreciate you taking the time to read and give some thought to this. If you guys have other questions for more information or anything that I can get to you for more elaboration on the symptoms, I will do my very best! This is my daily, and I won't be able to break it down again until next weekend as long as it remains able to get me to work and back haha.

This is the last gremlin (hopefully) before I can finish my car and call it a wrap. For now

turtle64b

Update for you guys following this; compression test results:
262 for the highest cylinder
242.5 for the lowest cylinder
8.04% disparity between highest and lowest