The Second Vatican Council (Lumen gentium ## 61-62), said:
... in suffering with Him as He died on the cross, she cooperated in the work of the Savior, in an altogether singular way, by obedience, faith, hope, and burning love, to restore supernatural life to souls. As a result she is our Mother in the order of grace.
This motherhood of Mary in the economy of grace lasts without interruption, from the consent which she gave in faith at the annunciation, and which she unhesitatingly bore with under the cross, even to the perpetual consummation of all the elect. For after being assumed into heaven, she has not put aside this saving function, but by her manifold intercession, she continues to win the gifts of eternal salvation for us. By her motherly love, she takes care of the brothers of her Son who are still in pilgrimage and in dangers and difficulties, until they be led through to the happy fatherland. For this reason, the Blessed Virgin is invoked in the Church under the titles of Advocate, Auxiliatrix, Adiutrix, and Mediatrix. This however it to be so understood that it takes nothing away, or adds nothing to the dignity and efficacy of Christ the one Mediator. For no creature can ever be put on the same level with the Incarnate Word and Redeemer...."
We notice that Vatican II did not add the words "of all graces." However, as many papal texts point out, Mary's role in dispensation flows logically from her role in acquiring all graces. Further, the Council itself added a note on the above passage, in which it refers us to the texts of Leo XIII, Adiutricem populi, St. Pius X, Ad diem illum, Pius XI, Miserentissimus Redemptor, and Pius XII, Radiomessage to Fatima.
Leo XIII, in the text referred to, spoke of her, as we saw above, as having "practically limitless power." St. Pius X said she was the "dispensatrix of all the gifts, and is the "neck" connecting the Head of the Mystical Body to the Members. But all power flows through the neck. Pius XII said "Her kingdom is as vast as that of her Son and God, since nothing is excluded from her dominion." These and many other texts speak in varied ways of Mary as Mediatrix of all graces, so often that the teaching has become infallible. https://www.ewtn.com/faith/teachings/marya4.htm
And there's more if that's not enough.
Again, this is why Christianity rejects roman catholic "tradition" on this topic and many others.
Christianity does not reject Catholic Tradition, heresy rejects it. Catholicism is, was and will remain the one, holy and apostolic Church from which all others split. The Church was first called Catholic in Acts 9:31 (ekklesia kath oles) before it was even called Christian in Acts 11:26.
These and many other texts speak in varied ways of Mary as Mediatrix of all graces, so often that the teaching has become infallible.
Thank you for providing this information. It illustrates my point that not every statement from a Catholic is Sacred Tradition. As much as Fr. Most would like, all of the texts that he referenced taken together do not represent infallibility. Mary as Mediatrix of all graces is not a dogma of the Church and there does not appear to be a great desire by the Vatican to make it dogma.