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The Sedevacantist Diamond Brothers from which all this nonsense arises from, are renowned for splitting hairs and twisting things to fit their own private narrative.

What a total pack of lies.  There are many R&R types who reject the validity of Conciliar Holy Orders, and I know several such priests, and faithful Catholics were questioning the validity of the Orders long before the Dimond Brothers even knew what sedevacantism was.

If you present yourself as a credible participant in the debate, then you need to stop vomiting forth logical fallacies, distortions, and lies.

The main argument being made on this thread is that the SSPX have turned modernist because they do not re-ordain every NO priest that either joins them or works with them.

Another lie and distortion.  Main point of this thread is to expose the fake priests that the SSPX are imposing on the consciences of the faithful for purely political reasons, since they can't afford to offend Rome.  There's absolutely no reason whatsoever that conditional ordination of all Novus Ordo presbyters should not be mandatory ... except that SSPX can't do that lest they offend Rome, since they're desperately attempting to effect a return tot he Conciliar collective.

In the past, SSPX have nearly always conditionally ordained, without engaging in some charade of an "investigation" ... as if "intention" can be investigated.  Pope Leo XIII taught the opposite in Apostolicae Curae.

Now, it is true that they used to hedge their bets by BLAMING the uncertainty and doubt on ambiguous formulae combined with unknown / uncertain intention, since they were afraid to commit to something that might lend itself toward sedevacantism (which they hate with a passion) and yet wanted to come up with some plausible-sounding justification for why, as a matter of course, they always conditionally ordained Novus Ordo priests.  But the general policy was to ordain conditionally ... as has been made quite clear from the citations presented here from +Lefebvre as the years went on.  Alas, there was one tragic incident in which +Lefebvre tried to impose a Novus Ordo Fake Priest, a Mr. Stark, in the early 1980s, but that occurred when +Lefebvre was probably as liberal as +Fellay is today, begging to simply make the "experiment of Tradition" while accepting Vatican II in the light of Tradition.

As for SSPX turning Modernist, there's a mountain of evidence for that outside of this issue and entirely independent of it, which Sean Johnson thoroughly cataloged in his book.  It's clear that they most certainly are slouching Modernist, right down to promoting that heretical Modernist book by Paul Robison.

Neo-SSPXplainer would do well to read: https://www.cathinfo.com/sspx-resistance-news/catalog-of-compromise-change-and-contradiction-in-the-sspx/