How is an invalid marriage contract renewed, and is a new mahr required?

According to the Shafi'is and Hanbalis, the صيغة (formula) for marriage is not valid unless it uses a word derived from "tazweej" (marriage) or "inkaah" (marriage). As for the Malikis and Hanafis, they consider the marriage valid with any expression that indicates perpetuity, such as "I have married you" (أنكحتُ), or "I have given you ownership" (ملكتُ), or "I have gifted you" (وهبتُ), along with the mention of the dower (sadaq). Some jurists made an exception for marriage, stating that it is not valid except with the words "nikaah" (marriage) and "zawaaj" (marriage) and their derivatives, as maintained by the Shafi'is and Hanbalis, out of worship and caution.