Brake caliper leak

[V12T]

I have a fluid leak from the two way check valve in the centre of my rear caliper. See pic. Does anybody know how this valve works, why it could be leaking and if it can be replaced.

[70chall440]

Looking at the diagram, there shouldn't be any fluid there I would not think.

[V12T]

I do not understand this. All the components are in the caliper. This two way valve just looks like a rubber bung from the outside and is loose. Cannot see it from the inside. If I pour fluid into the back of the piston it drips from the rubber bung. Pressure on the bung stops the fluid. I cannot see how it comes out and am reluctant to try until I know how. What is it's purpose? I presume it needs replacing? Can it be replaced?

[70chall440]

Can you get parts for this caliper? If so, get a new piston and replace it. Either that or replace the whole caliper and be done with it.