I watched GF3 again and I noticed that Michael imparted a lot of advice to Vincent but forgot one piece of advice his Father gave him.

Don Altobello got in Michaels car and suggested that there should be a meeting to calm things, get everyone together, which resulted in the helicoptor hit. Afterwards Michael was trying to figure out who the enemy was and only did so when in the throws of a diabetic stroke. He should have remembered the advice he got in his Fathers tomato garden many years earlier...

VITO CORLEONE
Now listen -- whoever comes to you with this Barzini meeting -- he's the traitor. Don't forget that.