mira shower - probably 20 years old - unable to turn off completely - is there a replacement washer and if so, is it easy to change.

Howell, December 2019

https://www.showerdoc.com/mira-excel-wall-and-deck-bath-shower-mixers-shower-spares

sdvvdsdv, December 2019

Depends on exact model, but normally you'd be looking at buying and replacing the cartridge within the shower valve body. A search online for Mira Excel Cartridges will help you identify the correct part. Not a hard job to do as long as you can isolate the hot and cold water supplies.
It will probably look like this:

https://www.showerdoc.com/mira-excel-1990-96-cartridge-903-33?channable=e79264.Mjg1ODk&gclid=EAIaIQobChMI9dfj2PK65gIVmpntCh3NqAU7EAQYASABEgLAW_D_BwE

Rupert, December 2019