I'll turn their own medicine back on them: it is manifestly plain (to me) that the "Reformers" did err.
Entirely possible. They have stated as such in their confession. No human institution is infallible. Nothing in the Bible says that any human or human institution is infallible.
As a protestant I have no trouble believing and trusting in a perfect, infallible God handing His Church over to undershepherds who are sinful, fallible men. Otherwise I would be tempted to worship these men, a form of idolatry.
I prefer to kiss the Son lest He be angry (Psalm 2) than kiss the ring or feet of a prelate.
I'll stick with the Bible.
Not as an RC you won't. You need the Magisterium to tell you what is right to believe.
So when I go to the Magisterium, and they point me to Scripture (Dei Verbum, Vatican II):
Therefore, since everything asserted by the inspired authors or sacred writers must be held to be asserted by the Holy Spirit, it follows that the books of Scripture must be acknowledged as teaching solidly, faithfully and without error that truth which God wanted put into sacred writings (5) for the sake of salvation. Therefore "all Scripture is divinely inspired and has its use for teaching the truth and refuting error, for reformation of manners and discipline in right living, so that the man who belongs to God may be efficient and equipped for good work of every kind" (2 Tim. 3:16-17, Greek text).
... I'm back where I started.