Pitts yes I think you are correct in what you say. For the May ditching, the correct manufacturer's procedures were followed, therefore the operator cannot be blamed for failing to follow the rules.
But at the time I was told by our engineers that they would have dropped the sump to have a quick look, rather than presuming it to be a false warning and dispatching it again having re-washered the sensor, and certainly on the second warning. Whether that is a case of hindsight or that is what would genuinely have happened I can't be sure.
But, trying to apportion blame aside, with the hindsight that we now have that accident was technically avoidable even if the manufacturers procedures did not cater for it. Of course they do now and so future such events should be detected before becoming critical... But of course we are not going to put that to the test it seems!