What is the ruling on the imam repeatedly reciting certain surahs from Juz' 'Amma every day and every year because he has not memorized the Qur'an?

The most deserving of leading the prayer is the one among you who has memorized the most of the Quran and recites it best, based on the Prophet's (peace be upon him) saying: "The people are led in prayer by the one among them who is most skilled in reciting the Book of Allah..." However, praying behind a man who repeats specific surahs is valid, and repeating surahs is permissible.