Do I need to go back to the Honda dealer?

My 2012 Honda Jazz/Fit had a noisy manual transmission and was difficult to select the lower gears. Honda replaced under warranty everything inside the gearbox (it took 4 weeks to get the parts from Japan). It is starting to make a sound like a bus again and is hard to select 2nd and 3rd again. This time the dealer said they all make this sort of noise (but wouldn't show me one of their cars making this noise!).
So my question really is, 'How do I make them fix it again?'. It's still under warranty.

Btw: I have always driven manual cars and never had a problem. It's definitely not me.

If it is still under warranty then I would choose a different dealer and ask about other cars like yours for the same problem.

Contact Trading standards. They have people who are experts, sounds to me like the dealer is trying to fob you off.
They can and will enforce legal action if they consider mal practice by the dealership. Do not go to a different dealer as this could jeopardise any claim that you may have.