Looking at your first pic. There is definitely something in that antenna socket on the threads. I looked at a few 800 here and they all look like the right one. My guess is something has threaded down in the base there.
*EDIT*
OK, so I looked again with a bright light, and using a sharp metal pin this time, not a tiny screwdriver, I was able to pick around and to my suprise, like so many of you suggested (thanks!) I dislodged a white plastic/nylon/Delrin (whatever) that was smashed into the lower threads. I truly thought it was part of it, as there is white down in the bottom around the pin. Fooled me.
Mystery solved. Just took me a 3rd try and digging with a sharp pin to realize my eyes were lying to me. It was so thin, and covering the bottom
threads so nicely it looked like it was supposed to be there. UGH
This is what I dislodged with the sharp pin, before I dug it out:
And here it is..really thin soft plastic. Whew! Finally solved.
Thanks for everyone's help!