Final follow-up -
I was able to fairly easily remove the antenna motor assembly from underneath the car after jacking it up 6" or so and supporting the car with a jackstand and a 6x6 block underneath the pinchweld seam, and having the rear tire rest on a number of short pieces of 1 1/4" board (nothing like being too safe). The assembly only really required removal of two hex bolts securing it to the support bracket and removal of one Phillips head screw from a grounding cable. Then just gently pull and slightly rotate the unit down through the grommet on the fender.
I could pull it down far enough without removing any electrical supply wires or the antenna cable to remove the three Phillips screws holding the case together and easily remove the broken segment of cable inside. Then it took another 2-3 min. to place it back in position and screw it back in place. As an aside I could clean up the ground connection which improved my reception a bit with a little less static.
The hardest part of the whole repair was to get the cable to grab and get itself pulled inside the case, which took a few times of manipulating it and pushing it in until the cogged wheel grabbed it.
Overall the job was actually quite easy, the longest part of it was to jack up the car and get all the supports in place for safety.
I see no reason to remove the wheel and fender liner, the access from below is quite easy and the exposure and visibility could not be better.
So for the time being, now I'm happy 'till the next thing eventually happens.
