Mira 453.05

A: There is a lip with a rubber gasket in it.

A: http://www.showerdoc.com/shower-spares/mira/MIRA-453-22-Mira-Stud-Wall-Fixing-Kit-(push-fit-tool,-3xScrews)-453-22

This is the key that you could use to remove the knob, but if the shower is old and out of warranty then just remove the center part of the temperature knob ( there is a paper cover on the screw) and unscrew the screw. There are other screws around the cover to be removed. Best to check the power button for damage before using the shower.

A: 

My recollection is that theknobs should just pull forward and off

A: I am not sure which part you mean by the case inserts. If you mean the lugs that hold the front cover to the back these are part of this item.

A: 

I am not sure which part you mean by the little plastic bit, however the cover comes with the button and the plastic lever that operates the switch.

 

A: Yes this includs the Button