Model year and mileage could be useful to guess what is going on.
BTW, I am no mechanic nor car expert. I am just a new Volvo owner who is struggling to keep my car on the road. What I notice unusual from my experience is that your LTFT is negative while you get rich condition code.
If it was from vacuum leak, I would expect a lot higher LTFT, as ECU would trying to compensate un-metered air.
So, what I would rather guess is something like this
Well, I have to admit that this still does not make clear sense because your problem is under idling not under boosting.
In addition, if I have to use silicone sealer, I would use sensor-safe one.