Gilbert signed a guaranty for the benefit of his son with Cobb Exchange Bank. The guaranty included

Question:

Gilbert signed a guaranty for the benefit of his son with Cobb Exchange Bank. The guaranty included all extensions and renewals of the son’s obligation. Subsequently, a renewal of the note added an additional $600 to the original obligation. On the son’s default, Cobb Bank brought suit on the guaranty. Who should win? Why? [Gilbert v Cobb Exchange Bank, 231 SE2d 508 (Ga App)]