First, you don't have to remove the fender to replace the antenna. Second, you can test the antenna to see if it has a broken cord or not without removing it from the car.
To test the antenna, unplug the three wire connector near the passenger hood hinge. There will be a green wire, white wire, and grey wire. Unplug the connector. Apply battery voltage to the WHITE wire, and ground the GREEN wire. This will make the antenna go down. Motor should run a few seconds and shut off. If motor will not shut off, then cord is broken. To make the antenna go up, put battery voltage to the GREEN wire, and ground the GREY wire. Again, motor should cycle off. If not, cord is broken.
Now, to remove the antenna follow these steps:
1. At the bottom rear of the inner fender is a removable panel. It is held in place by two torx screws and some clips like those used on door panels. You will also need to remove some of the screws holding the wheel opening molding to pull the panel down and off.
2. On the inside of the fender just below the hood hinge is a 10mm bolt. This holds the antenna bracket. Unplug the antenna lead connector and unplug the three wire connector. Lastly, remove the two 9/32" screws holding the top of the antenna to the fender.
3. Now fish the antenna out of the hole where the lower panel was removed. I find it easier to turn the antenna 180 degrees before pulling it out.
If the cord is broken, most of the time to mast cannot be pushed down because the cord gets out it's "channel" and acts like a brake.
You cannot use weed wacker cord to repair these antennas, as there is too much torque from the motor. The weed wacker cord is not stout enough to trip the limit switch, and instead the cord will wrap around itself inside the pulley. Although the motor will finally stop, the cord is getting damaged each time and will eventually bind the motor completely.
I have not heard very favorable reports from the generic Delco replacement, and the cost that the dealership charges is excessive to R & R these antennas. A local repair shop would be better, especially if they know how to the job.
I sell original rebuilt antennas for these models for $125 with exchange. Includes a reproduction mast and a one year warranty.