Anyone interested in the "SSPX Question", might want to take a look at an entry on the blog The Sensible Bond by a frequent commenter here, Dr. Brian Sudlow.
I’ve made the journey, and this is how.
Imagine me in 2003, a younger and certainly a thinner chap, on the point of completing the translation of the biography of Archbishop Lefebvre (ABL from now on). It was a monumental task which I still feel honoured to have undertaken, for however one disagrees with ABL, he was for most of his life an undoubtedly great servant of the Church. His errors, when they were errors, were made out of love for the Church. It was about this time that Fr Paul Aulagnier, the very first seminarian to ask ABL for help in the late 1960s, and these days with the Institute of the Good Shepherd, was drummed out of the SSPX. There were various reasons for this expulsion but one of these was an interview he gave to The Remnant in which he said something that, for once, broke through my traditionalist view of the Church: he said that on their current course, the SSPX were on, or risked following, a schismatic trajectory.
There is a lot more.
It is very engaging.