I do not think the pendant makes a straight run from bridge deck down into the CB trunk. You can see the metal tube from inside the cabin looking under the bridge deck, and it makes a curve.
I think I would fashion a metal "J" hook and reach up inside the aft end of the CB trunk and try to hook on the top of the board and pull it down. Some people have taken a thin piece of metal and tried to run it down the sides of the CB trunk hoping to scrape out crud. There either has to be a lot of crud, or your CB might be swelling from water ingress. Hope you get it figured out.