I am trying to dismantle my Mira 723 shower. When I remove the flow control knob, I am unable to remove the flat washer, wavy washer and temperature knob as they will not pull over the end of the spindle as there is a fixed plastic grooved cog fitted on it. This cog slots inside the flow control knob. Numerous attempts to remove the plastic cog have proved fruitless.
Two years on, and I had exactly the same problem and was delighted to read the advice above. However, the new Mira knob was too tight to fit on the old spindle. I had to drill it out to a larger diameter first, but now all seems OK.