I replaced mine with a new mast, $38 from the Nissan dealer. I just had someone also sitting in the driver's seat turning the radio off and on to first pull out the old mast, and then threading in the plastic "cable" for the new one.
I had trouble that the new antenna wouldn't contract fully, so I cut off some of the plastic "cable". That was a mistake. Then I had to crimp the last section of the antenna so it wouldn't run to the end of the threaded cable. I think if I had been patient and let it work the antenna a few days it would have contracted fully.