Muhammad Baqir Majlisi
Muḥammad Bāqir b. Muḥammad Taqī b. Maqsūd ʿAlī al-Majlisī (Arabic: محمد باقر بن محمد تقي بن مقصود علي المجلسي) (b. 1037/1628-29 – d. 1110/1699) known as al-ʿAllāma al-Majlisī (Arabic: العلامة المجلسي) or the Second Majlisī (Arabic: المجلسي الثاني) was among the most famous Shi'a scholars in fiqh and hadith and lived during the Safavid era.
Allama Mohammad Baqir al-Majlisi is a great scholar in the Hadeeth sciences and he compiled the well known collection of Hadeeth in his famous book Biharul Anwaar. He has written others books as well. His grading is according to his own research and Ejtihaad. Other scholars have their grading which can be like or different from his grading as all the Mujahid scholars are free in their research in the narrators and narrations.
Al-Kaafi book has the most authentic collection of narrations of Hadeeth but we don't say that every narration in al-Kaafi is equally authentic. The expert scholars have their right to study and verify every narration.
It is the consensus of the Shi'a scholars that there is no distortion in the Qur'an. You can read more about this topic in the article below that gives references to the statements of a variety of scholars.
A famous scholar Ayatullah Sayyid Abu'l Qasim al-Khu'i has a detailed discussion around this topic in his book that you can also go through for a more in-depth treatment of this subject.
Not at all.
All prominent Shia Scholars believe that Quran is intact and never been distorted.
Shia enemies put false allegations on us including in this matter. If they read our books properly, they will see that our faith is that Quran is intact. Sunni books have narrations from Omar that Sura al-Ahzaab was like Sura Baqarah, and from Ayisha that a Quranic chapter was eaten by a pet. These Sunni narrations and any similar narration are rejected by us because we believe that Allah (SWT) has promised to save and protect Quran from any discretion. (Sura Al-Hijr, verse 9).
We do believe that many persons tried and still trying to twist the meaning of some Quranic verses to make it in accordance to their wrong claims, but Qurani'c words are intact.
Shia scholars have written books on this subject confirming our faith in the intact Quran.