Its low tech, but it works; a roll of aluminium kitchen foil - ideally use just the former after the aluminium has been all used, or a cling film former, or a baking paper former, etc

Place one end where you think the leak is and the other end to your ear

If you are using a former with aluminium foil still on it, it is safest to unplug the machine first as you are using electrically conductive material

using one of these formers will allow you to quickly locate the source of the leak

the two main culprits are of course the safety valve and the anti-vac valve - it is highly unlikely that you will have a leak at a fitting