Geberit Twico 1 SHORT VERSION. This dual flush valve by Geberit is exactly the same as the longer version except for the height. Check the dimension carefully as the taller valve is much more common.
Geberit part number 222.260.00.1
(Tall version can be found here: https://toiletspares.com.au/catalog/product/view/id/24/s/geberit-twico-1-complete-with-button-etc-product-code-ats-068/category/19/ )
It includes all ancilliaries including buttons, bridge and push rods.The Twico valves unclip straight off the basket and are a direct replacement without removing the cistern.
Remember, when replacing the flush valve, it is a good idea to also replace the inlet valve. These items have a similar lifespan and you don't want to be doing this job twice.
Have a look at our inlet valves, they are probably much cheaper than you expect. (scroll down or look under “Inlet Valves” on the blue ribbon above).
Also, for adjustment of your valve, have a look at our page explaining how they work. This will give a good idea of how to adjust them. Start with the single flush valves and then read about the dual flush valves.
The explanation is here: