I was asked by a customer to look at their mira 88 shower as the control knob was too stiff for him to use. I have replaced the internal on off control and the temp control. putting it back together I have had trouble when screwing on the outer brass casing. this seems to be pressing against the on off control and making impossible to turn. having sorted this out by making sure the on off control didn't move as i put the casing on. The shower then worked fine, except for the fact the temp control was very stiff. I turned the temp control a few times which losened it a bit, but when i then turned on the shower it woild not shut off again. can anyone help with this?