Ducati Diavel Workshop Manual page 626

Cooling system: coolant expansion tank
Loosen the clip (28) to release the breather pipe (27) from the half-casing.
Loosen the screws (32) and remove the fitting (33).
Recover the O-ring gasket (31) located between the retainer and the vertical head.
Loosen the clips (21) that secure the pump/radiator sleeve (22) and the radiator/radiator sleeve (23).