'Oxygen free' wire is suppose to not corrode internally, but Ive seen it happen. Most often, it corrodes at the ends where the jacket has been stripped to connect to the batt and/or amp. This corrosion expands the wire diameter, allowing oxygen to seep deeper up the cable, which allows the corrosion to go deeper. If the corrosion isn't too severe yet, many times you can just cut off the end of the cable and it will be fine, but Ive seen some wire that was corroded almost all the way from one end to the other.