Easy way to check for boost leaks on a G40:

-Disconnect the BRV/throttle linkeage
-With the engine running, close the BRV linkeage for no more than a second or two at a time
-This will cause the boost pipes to pressurise - if there are any leaks, you will hear them. Just listen to where the noise is coming from, then use your hands to pinpoint where the air is rushing out from.