Correcting the Imaam in fardh Salaah

Q: What is the correct procedure when a Hanafi imam makes mistakes or gets stuck during qiraat of the fardh salaah? It occurs often with our imam reciting his weak portions in our fardh salaahs with many times him repeating the same aayat 6/7 times as he cannot continue. Are we allowed to correct? Or should he proceed into ruku? Even if someone does correct he tends to need the same lukhmah a few times before continuing.