For some reason my kindle wont let me play half the you tube videos i click on, and yours happens to be one. Lol. Anyway, best way to pinpoint is with a stethoscope. Make sure the airflow changes slightly or you hear an electrical type click when you change the ipr, that tells you the ipr is working or not. If it is a large leak, it should be fairly easy to find with a stethoscope, just take the metal tip out, and find where the air is coming from. A small inspection mirror and a flashlight will also make things easier.
Good luck.