Very good. Now read those quotes, and compare them with your: the Church can commit theological errors regarding the faith but it will be "harmless" and won't damn you if you follow it; the Church can't be "substantially corrupt;" the Church can't commit "substantial error." Then compare it with what I said in post #222 of this thread:
Since it's getting exceedingly tiresome reinventing the wheel with you, I'll close with what I said in another thread on this issue:
Why don't you go post something from some other real sources about "indefectibility": it will do more damage to your novel position that the Church could commit such blunders as BOD (justification and salvation being possible without receipt of the sacrament of baptism) about the Gospel of the saving grace of Christ that it was given charge to preach.
Utter nonsense and novelty.
Ridiculous, characterizing the notion that the Church's Magisterium cannot become corrupt as novelty. We have consistent teaching of the Popes and the Church Fathers, Doctors, theologians, that the Magisterium cannot be stained with error. Yet no theologian holds that the Magisterium is ABSOULTELY free from error. So what does it mean for the Magisterium to be free from error and not stained by error? It means that it's substantially or essentially free from error, even if there can be some error there
per accidens. That's the distinction, and Msgr. Fenton, in the passages cited, articulately expressed the threshold between fallibility and infallibility, which you continue to ignore.
Proposition I: Magisterium is free from error and all stain of error [taught above by the Popes ... which you reject]
Proposition II: Magisterium is not absolutely guaranteed to be free from error [taught by all theologians]
So then this apparent contradiction requires a distinction for both of these to be true. That distinction is substantial vs. accidental, or as Msgr. Fenton characterized it extensive and harmful.
You reject Proposition I above by attributing the doctrinal corruption and the corruption of the Mass to the legitimate authority of the Catholic Church, and that's heresy. You keep throwing the word novelty out there, but I defy you to find any Catholic theologian ever who agrees with you that the Magisterium can go off the rails so badly that it justifies severing submission to and communion with the Holy See.
THAT is novelty, not my (and Msgr. Fenton's) distinction to reconcile the notion that the Magisterium is inerrant and unstained by error, and yet not absolutely free from error. This distinction is absolutely common sense.