Rarely do the intercoolers on our cars have problems. When they do have problems it is under sustained high boost. That high boost being around 18 psi and from months of this kind of boost the plastic end tanks will give.

If you wanted to test the intercooler, I would use some kind of rubber hose, big enough to fit over the big outlets, and plug those with something non flexible. Like a plastic PVC end. So in essence u would use the rubber unions like they are in the car, but with PVC ends where the hose would be.
Then I would find some kind of fitting that would thread into the drain plug and allow you to fill it with compressed air. This would allow you to find the smallest of leaks and under pressure as well.

The simplest approach would be to clean it and see if it leaks from anywhere but the outlets.

I would personally check all the hoses. Especially the rubber flex ones that join the intercooler pipes and the metal hoses. These have been known to look ok, but under close inspection reveal cracks that would only show up under boost.

I am like you also, very precautious. my car is only currently running 6 psi.
Friend and I intercooled it, so it was actually running 6 psi before intercooled. I could theoretically turn the boost up now since the engine ingests cooler air after the intercooler addition, but I not going to chance it.

But that is because I want it tuned well before I up the boost and make sure I dont grenade the rebuilt motor soon. (bought it with rebuilt motor)
I will make sure all my fluids are synthetic, the cooling system is working well, I have good mixture and a CBV welded in, then I will incrementally raise the boost.
What model car is it? 200s used rubber hoses a lot, the 90 degree rubber/flourosilicone/whatever they used is also prone to this kind of cracking.


take care
hope this helps

Luke
82 242Ti 167k miles