Nauticam RX100IV housing - well sealed?

I just realized that my nice & shiny NA-RX100IV housing has only a single o-ring at the door. This is of course some additional risk...

Other than the vacuum valve, is there any means to check if its well sealed? Being a full aluminium housing, there is no way to check visually...

Being one of the most expensive housings for the camera, "good for 100m", I expected two o-rings...

Get the vacuum valve as you have visual confirmation it is sealed. I have all 3 of my housings with valves fitted and they are worth every penny.

I'll do so. Any cheaper alternative than the Nauticam?

Get the vacuum valve as you have visual confirmation it is sealed. I have all 3 of my housings with valves fitted and they are worth every penny.

Thanks! I wasn't aware of the valve-only option, the full V4 is rather bulky for a tiny housing.

Besides, it seems to be easily adaptable to any other housing brand...