So let's review then....a brazillian search plane spots an oil slick more or less right over this newly discovered debris zone (correct). A french submarine is sent to investigate and finds nothing. Said submarine can find another sub in the worlds oceans, but can't find a data recorder (that wants to be found, due to emitting a signal on a specific bandwidth) that is more or less right next to it. Thermoclines and other known sonar deficiencies aside, for which sub sonar crews are trained, this one has more questions than answers.
Also, on the tech thread there are sonar pics of the debris field overlaid with the original search pattern and newly discovered debris field. They are so close that they were on the edge of this new find during the original search. The time taken for this new search to find the debris field was very short given the size of the search area, guess they were just lucky eh ! ......ummm !