Dust the inside of the housing near any controls that penetrate it with dry unsweetened grape Kool-Aid, then take it down to depth void of camera. Place a soft weight (two pounds) inside the housing in a sock (to prevent any scratching if you are concerned about that) for some positive buoyancy. The Kool-Aid is white when dry. ANY moisture will immediately and permanently turn it purple. Even if the moisture evaporates or is absorbed by your desiccant pack the leak evidence is preserved.

Rinse and dry the housing well before inserting the camera. A clear housing makes it easy to detect any leaks as you can see any purple stains even before opening the housing.