As far as how often camera's flood it is all about how you care for it. A freind of mine told me when I first got My Nikonos V, "It is not if it floods, it is when." That said I have done hundreds of dives now and I have never flooded the camera or strobes, so through proper maintence cameras do not have to flood.
As far as what causes a flood it is nearly always user error. When a Sea & Sea camera (and UK lights for that matter) is returned for flooding the tech will clean and lubercate all user replaceable o-rings and do a "pot dive" to 150ish feet and if it passes (no water in the housing) the manufactorer says it was user error and is not usually covered under warrenty.
Follow the manual as far as o-ring lubercation, because different o-rings require different amounts of grease. Also use lint free towells to clean the o-ring.
It is always a good idea to test a new housing without the camera, because it could be damaged in shipping, and insurance never hurts.
As far as what causes a flood it is nearly always user error. When a Sea & Sea camera (and UK lights for that matter) is returned for flooding the tech will clean and lubercate all user replaceable o-rings and do a "pot dive" to 150ish feet and if it passes (no water in the housing) the manufactorer says it was user error and is not usually covered under warrenty.
Follow the manual as far as o-ring lubercation, because different o-rings require different amounts of grease. Also use lint free towells to clean the o-ring.
It is always a good idea to test a new housing without the camera, because it could be damaged in shipping, and insurance never hurts.