The HEQ5 with belt mod is now running smoothly. The hardest part of fixing it turned out to be hauling it up to my upstairs office so I had somewhere quiet and dry to fix it and finding a few days where the clouds have cleared so I could point it at the sky to test it.
After an initial try of tweaking the backlash on the RA axis using astro baby’s guide the clicking still remained.
I briefly toyed with the idea that there might be a slight lump on the RA belt, which was reported in one thread, but this turned out not to be the case (just flip the belt over and see if the click happens in the opposite direction of travel).
So I reread the instructions carefully and did the job properly. Clicking disappeared. Movement appeared to be smooth.
My pipe-dream of making a laser spot on the wall to do a star cross test in PHD2 seemed like to much trouble and clear skies were forecast for that night so I just took the plunge and set it up outside and started taking test shots.