This is another way to finding boost leaks other than the tennis ball method. I've used this with good results on all my DSMs though the concept is the same for the 1.8T.
Originates from www.vfaq.com
How to build an Intercooler Pipe Pressure Leak Tester
A 4 inch long piece of 2.5" O.D. (outside diameter) hose. (I used some radiator hose I got at NAPA)
1.5" I.D. (inside diameter) PVC end cap.
2 band clamps that will fit around the 2.5" pipe above.
A valve stem (I used the rubber type you press in)
Note that if you have a larger turbo, the sizes of the end cap and hose may need to be larger in order to fit the turbo inlet.
To assemble, just put everything together as shown.
To get the valve stem in, I had to drill a hole in the PVC cap.
To use it, just remove the intake pipe from your turbocharger inlet, and attach this in its' place.
Now you need to hook something up to the valve stem to pressurize the intake so you can listen for leaks. I use a 7 gallon air tank I got from Walmart, I just fill it up with air at the local gas station. You can also use a simple bike pump.
If you have a manual boost controller hooked up, you might want to plug off its' intake hose, as they leak a lot of air, making it hard to pinpoint the real leak.
Pressurize the system, and listen all over for leaks. Make sure you or a friend listens under the bumper too, wherever there is IC piping.
A leak will be obvious, they make a loud hissing sound.
You might want to have a friend check out your boost gauge while you are pressurizing things, to make sure you don't put too much pressure on things. (20 psi should be safe, or whatever you run safely for boost)
Places I have heard of leaks occuring:
Intake manifold ports
Throttle Body gaskets
Holes in the intercooler
Holes in the intercooler piping (sometimes the rubber pipe inside the stock woven mesh pipes cracks, and you can't see it from the outside... the pressure tester will find it though!! )