Dual flush stopped working

[JohnHarrison]

It's a Thomas Dudley Vantage (TD 212-A) dual flush. Possibly getting on for 13 years old.
I'm not a plumber but I try to solve problems myself. I found members of this forum extremely helpful some years ago when I installed a replacement Mira shower - very proud of myself! I've had to sign up again because it's been so long!
I've previously repaired this toilet flush after noticing that the 'air tubes' had become detached. It's been working fine for at least 2 years.
A few days a go the flush had stopped working & I saw that one of the tubes needed reattaching to the 'cylinder thing' (sorry, as I said, I'm not a plumber!) in the middle. I checked that the other tube & the 2 that connect to the push button were secure.
Now the button needs a few presses & some nursing to achieve a full flush.
I may need to install a whole new system in which case I'd probably try to get the same model.
Thanks in anticipation of any advice.

 

[JohnHarrison]

Well, I've done it but I'm not completely happy with it. There are only 2 ways the valve will fit - 180 degrees apart - both of which cause the tubes entering the valve to get squashed against the cistern housing. The old valve was not like this. I've tested full & short flushes, both of which are not as responsive as they should be. Anyway, we'll see how it goes

 

[ShaunCorbs]

Any pictures?

 

[JohnHarrison]

Any pictures?

 

[ShaunCorbs]

Sorry of the tubes ?

 

[JohnHarrison]

Sorry of the tubes ?

I had to give my head a break from the job.
The new valve has snibs on which prevent it from rotating as far as the old one did. This meant that I could not avoid both tubes being bent at their exits against the cistern walls - restricting airflow. The full flush, however, was excellent but not the short flush.[The push button unit had a broken piece & was loose so I bought a new one & installed it.]
I knew I had to rotate the valve so that the tubes were not squashed but it's only today that I've had the confidence to tackle this. Using a pair of grips I loosened the large plastic nut underneath (had to put a mirror underneath to see)until I could rotate the valve. The tubes are now free. But even after tightening the nut, there is a leak - I tested with a small amount of water in the cistern after putting lots of towels under. There's another nut (more rounded shape) which may resolve the the leak but it wouldn't turn
Now I'm a stuck again so I've contacted a plumber but they've not got back to me yet. So everything looks ready for test apart from the leak. Here are some photos.

 

[ShaunCorbs]

Is it leaking when there’s water in the cistern or when flushed ?

 

[moonlight]

Take it back out and put it back in the same position as the old one was in, always tight. Did you check the button first?