Oil in intercooler lines

you can also use a smoke machine instead of soapy water. Don’t try to put the smoke inside the pipes, just fog engine bay while the boost leak tester is applied. It is very easy to tell where air is escaping this way. Sometimes the soapy water can be hard to see…

And if you don’t have a leakdown tester, you can just throttle your air WAY down at the regulator.