Here's a recent post by Called to Communion. Ironically, instead of constructing a successful analogy to sola scriptura, the OP inspired an argument against Roman Catholicism.
On the one hand, the RC magisterium is perspicuous. On the other hand, the Scriptures which the apostles wrote - yes, the same apostles who RCs argue constituted the RC magisterium in Acts 15 - are not perspicuous.
Is the RC magisterium necessarily perspicuous or not? If not, then how can one determine which teachings are and are not perspicuous? If so, then why isn't Scripture perspicuous?