Can anyone tell me if there is anything other than pulling the retaining clip that has to be done to remove the coupling (quick acting coupling/couplpiece Part # A1K0 122 291L), connecting the coolant hose and the radiator.. I see there is a coolant leakage from this part (perhaps the o-ring) but I am unable to remove it even after pulling or removing the retaining clip, darn stuck! Tried pulling and moving but it wont move at all, is there any other lock or somthing that has to be unlocked/opened?

cheers!