Octavia 1U 2004 pd130 6 speed clutch part identify

Hi - could anyone please identify this part for me ? It's part of the clutch inline from master cylinder to slave, and lives up against the bulkhead

in the engine compartment, directly above where the power steering pipe joins the steering rack. 

It's leaking, and the local dealer isn't much help. 

At first I thought it was the clutch delay valve, but I think that's adjacent to the gearbox (6 speed), with the slave cylinder inside the gearbox. 

Thanks in advance

Tom