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Whether or not a Council decides to issue a solemn definition, the understanding of the Church has always been that when a moral universality of the bishops (i.e. nearly all of them) get together and teach in union with the Pope, that the teaching is protected from any substantial grave error by the Holy Spirit.

^^^ False NO new doctrine. This is one of the diabolical new doctrines of V2, taught only in Lumen Gentium (#25.2) and is strictly the understanding of the V2 church, not the Catholic Church. This aberation of Pentecost is not to be found anywhere in Church teachings.  

25.2 Although the individual bishops do not enjoy the prerogative of infallibility, they nevertheless proclaim Christ's doctrine infallibly whenever, even though dispersed through the world, but still maintaining the bond of communion among themselves and with the successor of Peter, and authentically teaching matters of faith and morals, they are in agreement on one position as definitively to be held. This is even more clearly verified when, gathered together in an ecuмenical council, they are teachers and judges of faith and morals for the universal Church, whose definitions must be adhered to with the submission of faith. - Pope Paul VI, Lumen Gentium

^^^ False NO new doctrine. This is one of the diabolical new doctrines of V2, taught only in Lumen Gentium (#25.2) and is strictly the understanding of the V2 church, not the Catholic Church. This aberation of Pentecost is not to be found anywhere in Church teachings.  

25.2 Although the individual bishops do not enjoy the prerogative of infallibility, they nevertheless proclaim Christ's doctrine infallibly whenever, even though dispersed through the world, but still maintaining the bond of communion among themselves and with the successor of Peter, and authentically teaching matters of faith and morals, they are in agreement on one position as definitively to be held. This is even more clearly verified when, gathered together in an ecuмenical council, they are teachers and judges of faith and morals for the universal Church, whose definitions must be adhered to with the submission of faith. - Pope Paul VI, Lumen Gentium

Ridiculous.  You cite Lumen Gentium as your authority, from a Council that you reject as heterodox and/or heretical.

Besides that, you need to do some work on your reading comprehension.  This is merely saying that their solemn definitions must be accepted de fide and does not address the question of whether or not the Council can teach heresy and wreck the Church.  I've cited a PRE-Vatican II source which says that it cannot due to the overall guidance of the Church by the Holy Spirit due to the promises of Our Lord.

Your position is heretical, Stubborn, without any question.  You consider the Magisterium to be defectible.

does not address the question of whether or not the Council can teach heresy and wreck the Church.  I've cited a PRE-Vatican II source which says that it cannot due to the overall guidance of the Church by the Holy Spirit due to the promises of Our Lord.

But what does "teach" mean in the context of a council?  Or when we say the magisterium has "taught", does that not imply binding, unchanging facts (i.e. doctrine)?  What's the point of "teaching" something that isn't required to be believed?
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Example:  You go to math class and learn "math doctrine" (facts and truths which must be believed, else you can't do math):  2+2=4, 10x10=100, etc.
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You're saying that one can go to math class and learn non-fact/theory (does the number "Pi" go to infinity?  How many prime numbers are there?) and that such theory/opinion can't be wrong?  Yet, such theories/opinions aren't required to be learned to do math.  If they can't be wrong, why aren't they required?
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In the context of Catholicism, you're arguing that the non-infallible magisterium can "teach" (to use the term loosely) but such "teachings" aren't required to be believed, even though they can't be wrong?  It makes no sense.  Seems like a whole waste of time.  Can you provide an example of any such "teaching" prior to V2?
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The way I see it is the non-infallible Magisterium is supposed to re-iterate, re-teach and clarify the doctrines that have existed from Tradition/Scripture/Christ.  All doctrine was given to the Church in Christ's time, either explicitly or implicitly.  So the Magisterium's job is to "hand down that which has always been taught" and to clarify and re-teach when heresies and misunderstandings arise.  It does these jobs using either 1) solemn infallible statements (unusual), 2) non-solemn infallible statements (papal clarification that doctrine x is of Tradition/Scripture), or 3) through the ordinary teaching offices of orthodox bishops/priests/theologians who re-teach Truths which are the same "yesterday, today and tomorrow".
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The Magisterium is composed of past apostles/saints/popes/clergy and also current pope/clergy.  Scripture/Tradition/History are the tools used, but since the Magisterium is an "office", so only men can fulfill its duties.  So, for example, St Alphonsus' writings or St Thomas' Summa is (generally) part of the magisterium because they have been proven to be orthodox by their peers and by saintly clergy and approved by popes.  But not everything coming from a pope/saint is correct, so God gave us Church history to double-check orthodoxy.  God also gave us the Church Fathers who in many areas, all agree on doctrine, which they received from the Apostles, so we can be confident that our Tradition is orthodox. 
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When a pope is not acting in his official capacity as Authoritative Teacher 1) solemnly or 2) non-solemnly but still authoritatively, then he is 3) just a simple bishop giving us his theological opinion.  Same applies to all bishops/priests in the world.  If any cleric (including the pope) is not basing their "teachings" on orthodoxy from 1) prior doctrinal councils, 2) Tradition/Church Fathers, 3) non-conciliar dogmatic statements, or 4) confirmed Scriptural truths, then how can it be truly Catholic?  Where is this "teaching" coming from, that we must believe it?  What foundation is it based on? 
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There is nothing new under the sun.  All Church doctrine has been revealed to us.  The Assumption dogma was not new by any means.  And the yet-to-be-defined truth of "Our Lady, Mediatrix of All Graces" is still implicitly part of the Faith, even though the Church has not defined it as such.  V2 didn't re-teach, clarify, or re-affirm orthodoxy, so its conclusions are novel and uncatholic.  This does not jeopardize the Magisterium's function or sublime nature at all, for the Magisterium (i.e. the men of today) are not protected from error, just like 98% of such fell into error during Arianism.  What is protected by the Holy Ghost, until the end of time, is the ETERNAL MAGISTERIUM, which is all orthodox/Divine Teachings of Scripture/Tradition/Doctrine that Christ gave to His Apostles and which their successors have guarded for 2,000 years.