Minor mod completion:
I decided that two-and-a-half years with black duct tape
over the whole where the antenna used to emerge from the A Pillar is enough. I had thought I wanted to bondo and paint, but I want a more reversible solution, since I want to consider this as a way to wire in roof-mounted solar panels one day (if I ever do it).
So, I cleaned the old tape gunk off with "Goof-Off", took apart the OEM plastic fitting and cut some sheet aluminum to fit the hard rubber bottom grommet piece, drilled holes in the aluminum sheet for the OEM screws in the original spots, and plasti-dipped the whole unit with three layers to help seal it up. Lastly, clear silicone indoor/outdoor caulk around the out edge. Here it is, process and result. I'm confident it'll be water tight for years. There is also a layer of aluminum tape under the rubber grommet (can't see it, of course). PICS:
james