Fluid for this part on gearbox

Wee MK4 golf 1.4 16v.
What fluid goes into the piston onto of the gear selector? Part with black cap ?
I've changed the gearbox fluid but wondered if this was separate?

 

Looks like a breather to me,no oil to put in there,cheers

 

Does the piston not need fluid?

 

As above the black cap is a breather.

 

So the piston it sits on doesn't take fluid?

 

That's not a piston.

 

This part that goes in and out selecting gears?

 

It's lubricated by the gear oil in the 'box

 

As above, the black cap is the breather for the box. The round part is a spring plunger for gear location. The box is splash fed when is use with all parts being lubricated by this action.