I have a Mira Excel B type shower control and the flow control ring is
getting quite stiff to operate. The temperature control is fine. Is
there any way of easing the friction on the flow control ring? I have
tried loosening the central screw that holds the outer temperature
controller and this may have eased it all a bit, but I don't like to
do this too much for fear of upsetting the whole mechanism.

Any advice and help welcomed.

TIA
John