Is it your view that Magisterial teachings and documents are perspicuous? If so, are they perspicuous both outside of and inside the community they are written for? To adapt one of your paragraphs, Is it the case that many doctrines that some Catholics believe are clearly taught by the Magisterium are repudiated by other Catholics, while both parties maintain the same adherence to Roman Catholicism and claim the other is in error in their interpretation? I think you see where this goes....Where it goes is exactly nowhere. In the first place, even if true it would not invalidate the criticism of Protestantism's claims for the perspicuity of Scripture.
Secondly, I'm unaware of any claim by the Magisterium to the effect that its documents are "perspicuous" in some technical sense. Absent any demonstration to the contrary, the entire edifice of this criticism falls apart. Completely. Because if the Church doesn't make such a claim - as Protestants most certainly do for Scripture - then the tu quoque is without merit.
Thirdly, the reason why the issue exists for the Protestant is that he has nothing like the Magisterium to settle disputes. Oh, there are (in some cases) denominational courts, but the bottom line is that no individual Protestant is in any way bound by the decisions of such courts, except voluntarily: he can always pick up his marbles and go to some other Protestant community where his views are either irrelevant or welcome, or he can start one himself (I have known more than one genuine Lone Wolf Protestant, let me tell you). But the Catholic confesses and submits by definition to the authority of the Church for the resolution of such disputes. Now some will say that the Magisterium doesn't address every point of dispute. For example, Thomists and Molinists are both welcome within the Church. But it's not the Church's mission to settle every bone of theological contention amongst Catholics. The Church's mission is to save souls, and consequently she teaches those things which are necessary for salvation. But it is not the Church's mission to dispel all clouds of uncertainty relating to all theological questions. God is infinite, we are not, and there are going to be things that simply cannot be understood by us humans, and there are going to be disputes that are irrelevant to the Church's mission. By way of contrast, however, the Protestant has no one to tell him what things are necessary for salvation - not with any more than purely advisory authority. So he must resort to the Bible himself to attempt to identify them.
And this brings us to the fourth point: our circumstances are fundamentally different with respect to the facts of the Christian faith. The Protestant searches the Scriptures in order to know what it is that he must believe. But this is not the nature of the Catholic's relation to the Magisterium. He is already committed to believing what the Church teaches, because the Church proclaims the facts of the Faith. This is a given for him. He may indeed misunderstand things on some points or other, but so long as his sincere intent is to believe all that the Church proposes for belief, he is reckoned to have an implicitly valid faith. This is important, because not all are equipped to be students of theology. Not all have the education, or the interest, or the time, or the resources, in order to pursue it. And there is nothing wrong with this. This is not to say that he ought not to learn what he can, but he doesn't have to be a theology geek in order to be a faithful Catholic.
But the Protestant's circumstances are completely different. The facts of the faith are embedded, he believes, in a book, and he must extract them. He may rely upon the guidance of others (in which case, I might add, his condition is hardly different from the lay Catholic's, so that Protestant criticism of that lay Catholic's reliance upon the Magisterium is completely unjust), but whether he does so or not is entirely up to him.
More could be said than this. Obviously. But I hope that this will be useful in demonstrating that it's a complete waste of time for the Protestant to pretend that if there are issues for himself with regard to the claimed perspicuity of the Bible, the Catholic suffers the same things in the same way with regard to the publications of the Magisterium. To quote Hank the Cow Dog, "No, and No, and Heck No."
And if someone can tell me the correct spelling for "tu quoque" (is it 'tu quoque' or 'tuquoque'??), I'll be grateful.