Then I tried to replace the wire on the focus rectifier, but it was no use due to the molded cap. I didn't have a spare small size top cap, so I had to carefully remove the one on the tube and solder a bigger one on to it. This involves carefully grabbing the cap with pliers and slightly twisting it, so the old glue will break free of the glass. Then it's simple to desolder the cap, and replace it. I took the replacement one from a dead HO tube, and used epoxy to glue the metal cap onto the top. Then I used a normal size connector, some more replacement wire, and sealed the connection on the flyback with non-acetate RTV. I doubt there will be any leakage from there now.
Also, for some reason there was a 22K resistor in series with the anode cap lead. I couldn't find it anywhere in the schematic, so it was removed. There seems to be more range in the focus control now, so that's good.