Hi
Decided to change the seals and the cylinder liner its pretty dirty (compared to Paul Pratt YT explanation video)
Whats the reason for the dirt accumulation?
How to remove it?

Unless your water source has dirt somehow, you should not have dirt there. Scale is a possibility. You removed the liner or do you see the "dirt" when looking up into the group? Do you have pictures of that too?

Didnt remove the liner. I think its only a hit of scale and not dirt..
How to remove the scale from the liner?

Clear seals - never seen those before.

I don't see any dirt, a bit of white scale, but nothing serious.

The black appears to be Copper(II) Oxide. If you can't scrape the black off with your fingernail, then it is Copper(II) Oxide - which you want to keep as it is protective. If you really want to remove it, then Citric Acid works. You'd be exposing the brass, but that's only a small bit of brass and the Copper(II) Oxide should come back fairly quickly (again, a good thing).

As an aside, that doesn't look like a CMA group to me.

Thanks

Transparent seals.Now I' ve seen it all.
It' s a clean machine.

You could use a vinegar soak as well to remove scale with a good rinse. Depending on the machine and whether you use a puck screen grounds and oils can get sucked up into the group. It can look like dirt.

+1 on oxide not being a bad thing.