Is it obligatory to apologize to one's parents for every past act of disobedience (ʿuqūq), and is this a condition for repentance, or is their contentment sufficient?

If the questioner's situation is as described, he is dutiful to his parents and no disobedience is apparent from him. Assuming a slip occurred, it falls within the scope of God's forgiveness, as He Almighty says: "Your Lord is most knowing of what is within yourselves. If you should be righteous, then indeed He is ever Forgiving to the oft-returning [to Him]." And ignoring obsessive thoughts is the best remedy for them.