I have the housing for the S400 and the Amphibico housing for the Canon Optura camcorder. I have yet to dive the S400, but I've used the Optura in Yap and Belize. Most, if not all, failures are due to improper use with the o-ring door seal being the most critical. An old, dry, cracked, or twisted seal invites trouble.

Give the seal a visual inspection, -lightly- moisten with lubricant, button the camera up, then submerge it a few inches and look for streams of bubbles (bad!). Work the controls and look for more bubbles.

If you are snorkling take it down a few feet and look for bubbles. You will likely not see any and you can just shoot for the rest of the trip. Do the pre-swim submersion test each time you take it out and there shouldn't be any catastrophies.

It helps to develop an attitude that you are trying to do something attempted by few in an environment hostile to electronics. If you -do- have a flood, it was in an attempt to do something novel.