Can't remove toilet flush valve

[Steve111111]

There's a small leak from the cistern into the toilet. It has a dual flush valve. I'm not a plumber but my own research on Google suggests that the rubber seal at the base of the flush valve is worn and needs to be replaced.

I'm struggling to remove the valve. I've tried to twist it but it's not moving and I'm afraid of applying too much pressure and breaking it. I've seen on YouTube that other valve models can be removed by rotating anti-clockwise. Should this particular one be removable without having to remove the whole cistern. Looking for advice on how to remove it. Not sure if this matters but the toilet was installed about 8 years ago.

 

[CountryFan]

Looks like Ideal Standard/Armitage Shanks. It should undo by a bayonet style, if you can see if it looks like it will separate where I’ve indicated? Should twist counter clockwise

 

[blup]

Remove the whole valve, drain cistern first

 

[HERTS P&D]

https://www.amazon.co.uk/Rubber-Standard-Armitage-Shanks-SV01967/dp/B0DMM571QV/ref=asc_df_B0DMM571QV?mcid=58aa1881f18e36429341abd72315d67f&tag=googshopuk-21&linkCode=df0&hvadid=713942471233&hvpos=&hvnetw=g&hvrand=8758543481216431294&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006625&hvtargid=pla-2399247098852&psc=1&hvocijid=8758543481216431294-B0DMM571QV-&hvexpln=0&gad_source=1

Andy

 

[Steve111111]

Looks like Ideal Standard/Armitage Shanks. It should undo by a bayonet style, if you can see if it looks like it will separate where I’ve indicated? Should twist counter clockwise

Thanks mate. It came off when I applied some more pressure. That rusty water over the years I think likely caused it stick a bit.