Decided to go with the old adage "if it ain't broke, don't fix it." Tried pulling with a bit more force and it did start to move but I am not confident I can get another cable through so will leave well alone as the cable looks in quite good condition! Will replace the external cable and use block connector instead of what is fitted. Thanks for the replies, much appreciated, thank you! [
Use the old wire to pull the new wire through. You can solder them together, but don't create a big ball or stiff section. Solder it just enough to stay bonded together.
There is a special lube for pulling wire. Go to your local ACE or HOME Depo and ask the people in the electrical department. Put it in from the top and give it time to work its way down the first bend. Then use a syringe to reach into the base connection. The lube is made for this. DO NOT USE SOAP. The chemicals in soaps can dissolve the wire insulation over time and cause a short.
I used to work in a light manufacturing factory when I was at Uni, before everything went to China.
Normally all parts are made separately and screwed together. Metal to metal joints would have loctite, so will require a bit more effort to undo. So it should come apart.
Its possible they have been glued. But if its not working, then what have you got to lose.
It may be easier to use the existing wire to pull a sturdy string through, e.g. mason's line. Preferably something fairly slippery. Then use the string to pull the new wire through.
Part of the challenge is avoiding a big lump or edges that will get caught. You can strip back the wiring a bit and twist two conductors together to form a small eye. A bit of solder or epoxy will keep it intact. Thread the string through the eye and tie a reliable knot, e.g. a bowline. Or avoid pulling a knot through altogether by simply looping the string through and using enough length to pull the doubled string through.
Reverse the process to install the new wire. Use a sharp knife to relieve any edges on the insulation and jacket that might catch. Keep feeding the wire in while the string serves to guide it through.
Update on progress with lamp! I managed with some lubrication, string and perseverance to replace the 2core wire inside the lamp frame. I would now like to change the external wire to three core and earth the metal frame. Any suggestions on how to do this? Ideally earthed inside out of sight. I could drill a small hole in base and use a small brass screw but I would like to keep lamp as original looking as possible so am reluctant to do this. 3core live and neutral wires would be wired with plastic connector to 2core internal wire inside base leaving earth to be attached somewhere/somehow? Thank you for replies, much appreciated!