Dead cats and wonky RKAT values on 2003 996 C2

Hey gang, So, I got the dreaded smog notice when I went to renew my registration here in sunny California and it's time to figure out what's going on with my repeated cat converter efficiency codes. First, I'll preface by saying that based on voltages from four new O2 sensors, I'm pretty sure my cats are dead. I had swapped on a 200-cell x-pipe from Top Gear (don't do this, cust. service and warranty is non-existent) and that was either DOA or my car killed those too. Having recently swapped back to stock to eliminate variables, I now need to figure out what killed them before I spend a pile of money on new or good used cats. To that end, I hooked up the ol' Durametric and started looking at FRA and RKAT values. The RKAT shows that both banks think there's a lean condition and are adding 2.7 - 2.8% fuel (which, I think I'm interpreting correctly based on Tony Callas' tech explainer . So, seeing that, I disconnected the battery for around 20 minutes and then after hooking it back up, I re-checked. The adaptations were set to 0% at first but after around 10 minutes of idling and revving to around 3k, the RKAT values were back up to that 2.7% mark. Now, to me, this kind of lean condition and added fuel says vacuum leak to me, but the car starts and idles just fine. I don't hear any hissing and on spraying MAF cleaner around the engine bay as best as I can, I didn't hear any change in idle in either direction. My question to you all is two-fold. First, am I interpreting the data correctly? Second, do you think it's a vacuum leak and if so, where should I be looking? Lastly, I do think the cat converter efficiency codes started happening after I had the AOS and plugs done, but I don't remember how long after. A month or so, maybe? For context, my car is a 2003 C2 with 143k miles and an extensive service history. Coils and plugs were done a couple thousand miles ago with OEM parts. I have an Ultimate AOS setup as well and a BMC panel filter with Flat 6 intake resonator delete. The vacuum thing also makes sense to me because despite things running fine, I hear a very high-pitched whistle on the freeway in sixth gear coming from the engine and it comes and goes with load. I just don't know what it could be and it existed pre-AOS so I don't think it's related to that. Help!

Update, it looks like the long crossover hose for the AOS is leaking. There's oil all along the underside of it as it goes towards the passenger side of the engine. I had a shop do my Ultimate AOS install, so I haven't been this far into my engine before. I haven't noticed any real oil loss over the last 10 or 11 months since I had the job done and the top of the engine case looks dry, so the leak is slow enough not actually to drip, it seems. Could this be a cause for my possible lean situation and subsequent fuel trim issues?

Yes. Also @Porschetech3 has an updated crossover tube that makes replacement much easier.

That's encouraging to hear, particularly because sending it to the shop right now isn't really an option. Thanks, media industry layoffs!

Also, just as confirmation, here are a few photos of the oil. Sorry for the quality, but it's hard to get a phone in there. There's also kind of a surprising amount of oil in the intake which you can sort of see. And the corrugated pipe zip tied to the rear intake crossover is the AOS crossover, right? The corrugated zip tied tube is covered in oil for basically its whole length. This is heading down towards the AOS on the driver's side of the car. I would guess there's like a teaspoon or more of oil pooled in the intake manifolds.

U would test that new aos. It may have failed already.

I have Skip sending out his manometer test kit since I already have the UAOS installed.

Are you sure that is the cross over tube and not the plastic conduit for the starter cable? My crossover line was solid black hard tube except at the AOS end. Transition from flexible to solid Flex AOS

Pretty sure, and I asked Skip for confirmation, but it's likely that the hose needs to be done anyway since it wasn't done when I had a shop do my UAOS. I'm tired of dealing with this stuff so I'll try and do it all at once if I have to go through the trouble of lowering the engine and disassembling stuff.