Was it the inlet valve?
If the problem was the inlet valve, then the water level would have constantly been increasing, and overflowing into the hole in the middle of the cistern:
If you see something like the above, that is, the water line is not constantly above the hole in the middle, that means your inlet valve is probably OK, and the problem is likely to be the outlet valve.
How to confirm the Outlet Valve is the problem
Get a torch, and shine it into the hole in the middle.
When I did this, I saw water was flowing where shown in the picture above! Voila, there was a fault with the outlet valve. The outlet valve is basically a rubber washer that stops water flowing into the pan. It is released when you press flush.
So what now?
You want to replace the outlet valve. Just watch the video:
Once the mechanism is removed:
Just yank it off:
Compare the old flush valve, on the right, with the new one, on the left … no wonder it was leaking!:
I used some tap lubricant to help reattach the new washer, as it’s a bit of a struggle to get it back on (but I don’t think this is strictly necessary):
And here you go – nice clean and evenly reattached flush valve:
Replace the dual flush mechanism, and check for success … there you go, no more leaking toilet!
If you are heading off to Bunnings to buy a new flush valve, ask for Item No: 9312232226167 or just print the picture below and bring it along! Not bad for $2.75.
Good luck with it all.