Just measured the outside diameter of my door tubes: just over 13mm.
I recently rewired my doors, including upgrading the live ‘up’ and ‘down’ and earth wires to the window motors. See my 3 Jan 2024 post on improving the window speed. I also used LEDs for the red door opening and white puddle lamps, less current.
Modern thin walled automotive cable is the answer: half the thickness of the Lotus originals so you can have more current capacity to the motors and still go thru the tubes easily…