I agree that NREC is almost certainly invalid.  So, even if you hold out some hope that the butchery of priestly ordination is valid, the number of priests ordained by bishops who had been consecrated before NREC is rapidly dwindling as time goes on.

To me, the fact that the ordination only made what appears to be a "trivial" change, in so far as it removes a single two-letter word in Latin, and since I believe that enemy infiltrators are behind these destructive changes, this only increases my suspicion that this was done on purpose with the intent to invalidate.  WHY BOTHER with this little word at all?  It's not as though its omission somehow "modernizes" the rite and brings some "fresh perspective" to it.  Pius XII when writing about the essential forms of these rites describes the essence of the form as invoking the Holy Spirit with a specific effect in mind, i.e. that they must invoke the Holy Spirit and call out the effect of that invocation, i.e. for the Holy Spirit to do [whatever].

Old Rite.  Renew in them the spirit of holiness (the Holy Spirit) SO THAT (the "ut") they might become priests.  Invoking the Holy Spirit to be sent in order to make the men priests.

New Rite.  Renew in them the spirit of holiness.  May they become priests.  This is not requesting that the Holy Spirit come down on them to make them priests.  It's two separate requests.  May the Holy Spirit come down on them.  May they become priests (addressed generally to God as a prayer).  There's no linkage between the action of the Holy Spirit being that which has the effect of making them priests.  Holy Spirit is involved in every Sacrament, and in the general state of a soul being in a state of sanctifying grace.

"May they receive the Holy Spirit so that the Holy Spirit might make them priests."

vs.

"May they receive the Holy Spirit.  May they become priests (through some unspecified mechanism)."

This severs the concept that Pius XII called out as essential to the validity, the invocation of the Holy Spirit to a specified effect.

I find it interesting that a trend has developed in the R&R crowd. They tend to justify the R&R position by lowering the authority and the scope of infallibility of the Pope and the Papacy, while simultaneously increasing the “authority” (he was a retired bishop) of Archbishop Lefebvre. Remember, no matter how good of a person he was, he was not and never was infallible and he did make mistakes and wavered on certain issues throughout his years.

I think that argument is flawed and very easily countered, Mithrandylan, by the fact that a legitimate Pope is not free to impose illegitimate laws. He is not a law unto himself, he is the Vicar Of Christ. He has no power to revolutionise the Sacraments. This is no organic development along the lines described by St Vincent of Lerins. As The First Vatican Council taught in the Constitution Pastor Aeternus "The Holy Ghost was promised to the successors of Peter, not, that by his revelation, they might make known new doctrine, but that by his assistance they might guard... the deposit of faith". That is why, all these years, most Traditionalists of the R&R persuasion, including ABL and his Society, have held doubts about the rite, without denying the legitimacy of the Pope.

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There is such a thing as the disciplinary infallibility of the Church. It refers to the Church being protected from imposing something inherently defective on the universal church. A strictly invalid rite of making bishops would be, in my opinion, a plain violation of the Church's disciplinary infallibility. It is related to the Pope inasmuch as all infallibility ultimately springs from the pope. The absence of a pope is a sufficient theological explanation for how we get strictly invalid rites of sacraments.
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So Plentus, would you say that since the Church has never solemnly defined that she can only publish and impose valid sacramental rites, we must leave open the possibility that she can publish and impose invalid sacramental rites?

The new Form in Latin is, if anything, stronger for validity than the old Form in Latin (by the « et » instead of an « ut »), but vernacular translations need to be checked to make sure that they clearly express the grace of the priesthood to be conferred.

This doesn't make much sense to me.  If the "hierarchy" were "illegitimate" then how is it that "the Church" did this?  No, it's not possible for the Church, i.e. for a LEGITIMATE pope, to promulgate invalid or even doubtful rite for the Sacraments.  That would be tantamount to a defection of the Church.  In fact, this consideration, that a legitimate pope could not promulgate invalid Sacraments, is what led Michael Davies to conclude the NO rites to be valid ... despite otherwise having been inclined to doubt them.  But all this begs the question that the NO papal claimants are legitimate.

These questions about the validity of the new rites does in fact contribute to a feedback loop that leads people towards SVism.  If you hold the MAJOR that it's not possible for a legitimate pope to impose invalid rite, the more doubts you have about the rites, the more you also have to doubt the legitimacy of the papal claimants.  An implicit acceptance of this MAJOR is what drives a lot of R&R folks to reject any disputes regarding the validity of the new rites.

MAJOR:  Legitimate pope cannot promulgate invalid rites.
MINOR:  NO rites are invalid.
CONCLUSION:  Popes who promulgated them and continue to endorse them are not legitimate.

So you can question the MAJOR (as you and others have done) or you reject the Minor ... to avoid the SV position.  So the "anything but SVism" mindset is driving people to reject either the MAJOR or the MINOR above.

For me, this is where this particular argument stands:

MAJOR:  Legitimate pope cannot promulgate invalid rites.
MINOR:  NO rites are doubful.
CONCLUSION:  Legitimacy of the V2 papal claimants is doubtful.

But this is one aspect of the doubt about their legitimacy, when taken together with other considerations, it's almost morally certain that the V2 papal claimans have not been legitimate popes.

As I said, you have the same problem: the Church defecting. This is because not only does indefectibility encompass a hierarchy teaching universally, and providing the means of sanctification, without error, but it also encompasses the necessity of a hierarchy, a living "governing body." You limit the indefectibility of the Church to teaching/sanctifying, but divorce it from its essential attribute of governing, having a governing body.