Hey Gubi thank you so much for the reply.

We did not pressure test it. I'm sure that will be their next step too. Will take a look at the cap too.

I have been driving the car softly during this time, staying out of boost. Last night I drove the car hard hard for the first time since having these problems (open road, multiple 2-3-4 gear pulls), and I smell coolant when I come to a stop. It doesn't last very long, it goes away pretty quickly. This is what made me suspect it's leaking under boost. I am going to go out this afternoon and wrap a towel around the coolant tank to see if there is mist escaping that otherwise isn't leaving evidence.

I can't tell if the car is smoking under boost, I don't see anything in the mirror but I don't have a buddy driving behind me to confirm.

Update: Drove the car hard, full 200-210 coolant temp, there is no blowby from the radiator cap, the towel is completely dry despite the engine bay smelling of coolant.

I poked around and I can't see any wetness for the parts of the cooling system which are visible. Nothing on the pipes, radiator, expansion tank, what I can see of the water pump pulley, what I can see of the thermostat housing.

Next step is pressure test. God I wish the ****ing rental test kits had an adapter for this car. None of them do.