Thinking about Fr. Alvaro Calderon’s (SSPX) study on the new rite of episcopal consecration, which changed the form. Nevertheless, he concludes it is “very probably valid,” and therefore can sometimes be used.

Compare that strange opinion with this excerpt from the above article by Fr. Faber regarding the prohibition against receiving even “very probably” valid sacraments:

“ S]urely your reverence for the authority of St Thomas, backed as it is by Suarez and St Alphonsus, may incline you to admit principles of moral theology, which, with respect to the very questions of the succession and sacraments, may point out a line of conduct different from the one you are pursuing.
They, in common with the other masters of moral science, rule that in matter of faith and sacraments it is not lawful to follow even a very probable opinion, but that the safe and more certain side is to be followed; that there is a religious obligation on men to follow it: and the propositions, taking the other side, have been condemned by the Church in the pontificate of Innocent XI; and it is remarkable that even the bold proposition, condemned by him, itself denies the right to use the probable opinion in the case of priests' or bishops' orders.”