CVA Firebolt .45 cal ultramag muzzleloader
 

Father got this given as it was found by a friend of a friend's family. It's not been taken care of but wanted advice as we know not much about black powder. In the picture this piece which I think is called a breach plug seemed pretty messed up. Should it be replaced and if so is there a special tool to remove it and what's it called.

You didn't post a picture.