My project for tonight... Replace the antenna gasket.
I bought a cheap universal gasket off Aliexpress. The size is a perfect fit, but I don't think the style is the same as the original and they don't look so good. It should hopefully keep water out which is my first priority though.
Replacing it isn't easy. You need to remove the rear pillar trim pieces which isn't obvious how but fortunately mine had been broken so they just fell off. So I repaired these using my new $17 plastic welder and two-part epoxy.
Then remove the plastic square screw, and it also helps to remove one of the C-pillar trim pieces.
Then you can lower the headlining just enough to access things, but not quite enough to see what you are doing.
Then disconnect the wiring (not easy) and remove the antenna nut (7/8"), clean, fit gasket and then reinstall everything (also not so easy).
The blue and white antenna is not the final result. I also ordered a stubby antenna which hasn't arrived yet, but just screws on.