How can I remove this flush valve?

[Minimax]

I've got water trickling into the pan of a toilet. The cistern water level is nowhere near the overflow pipe, so I suspect there's a faulty seal at the bottom of the flush valve (a Geberit model). However, I am unable to detach the flush unit to check. There don't seem to be any side clips to press. Also, I've tried rotating the flush unit, and it moves about 90 degrees, before jamming against the cistern walls - but I have noticed that, while the main body of the unit turns, the pedestal of which it sits remains stationary (I've tried twisting the pedestal directly, but it won't shift). I've attached some photos to clarify.

Any ideas on how to remove this unit?

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[rpm]

Not come across one with clips to press, normally slight twist , ie from twelve O`clock to two O`clock and pull out.

 

[Minimax]

Not come across one with clips to press, normally slight twist , ie from twelve O`clock to two O`clock and pull out.

Any idea if the pedestal in photo 1 is meant to turn? I can't get a good enough view to tell if it's part of the flush unit, or just the fixed thing the unit plugs in to?

 

[ShaunCorbs]

The bottom part is fixed don’t try and turn this as will end up splitting the toilet to retighten it

 

[snowhead]

Twist and pull,

 

[Minimax]

Thanks for the replies. It took a lot of force, but the unit finally twisted off. As suspected, it was a faulty seal, now fixed.