You believe, as I do, that the Magisterium of the Catholic Church is infallible - when certain conditions are met (Pope Leo XIII, etc.).
However, you believe that the Magisterium of the Catholic Church is fallible when certain conditions are not met.
You're completely fabricating your own Catholicism making such statements. Nowhere does the Church teach that there are exceptions to the infallibility of the magisterium.
Nowhere. People in this forum love to say it because it helps them justify the errors of Vatican II, but it is complete nonsense.
I will ask again where you think the Church has ever taught there are exceptions to the infallibility of the magisterium, but no matter how many times this is asked, no one ever responds. No one responds because the Church never taught it. Go look at the list of quotes just posted about the magisterium.
There is no such thing as a General Council that teaches error. But there IS such a thing as a General Council that is illegitimate. There have been many illegitimate Councils throughout the history of the Church and Catholics need to start realizing this is the only logical explanation for Vatican II.