Completely understandable. Still don't like culling, which makes it harder when there is something good about a cockerel but.....
Fights happen without there being a health issue at all.
You said Heisenberg is a nice/mellow roo that is willing to let things be, right? Those are often the first targets of cockerels or other roosters that are feeling the desire to change their ranking.
Example, if he just postures and walks away instead of gives a good bop on the head, the "aggressor" can get bolder and bolder.. in his mind he is somehow pushing the rooster off.. it's feeding his instinct to go into a fight. Might still happen or might not still happen had the dominant rooster been more physical in his dominance every time.
Isn't Ozzy an cross? Often people think good things come out of crosses- vigor, production, etc... however negative traits can show up. It may be the cross giving him a dash of 'fight'. Maybe the australorp line has intolerant roosters and it;s showing up in him...
One other option? breed him asap then cull? Keep the daughters to stay away from potential fighty roos.