No such thing as a tiny leak most likely. Once it breached, the difference in force would immediately split the leak or rupture open in milliseconds, and the crushing force would be almost instantaneous.
12,000 feet is 2.2 miles. What kind of sonar did the mothership have? And more importantly, was someone monitoring the sonar at all times, and is there a recording of the live sonar? I'm betting no.
Also, if SOSUS picked up the implosion, the Navy may have kept quiet because they don't want their capabilities getting out. And as far as submarines breaking up and making noises, I think it would happen differently because those subs break apart at much shallower depths, and don't happen all at once. They have water tight compartments and they would go one by one. And any WWII sub is much larger than any deep-sea submersible.