[ertand]

I wonder what the procedure to locate the leak was.

[rsync]

You spray soapy water all over the outside of the module and watch for any spots that start bubbling.

[jacquesm]

Nah, you spray soapy water all over the inside of the module and watch where it egresses.

[LeoPanthera]

They use an ultrasonic detector that can hear the sound of gas being forced through a small hole.