coolant pipe coming out of engine block

Hi Everyone,
The cabin heater does not work in my X1/9 i've found a very corroded and blocked pipe which is stopping the coolant from getting to or returning from the heater matrix, its the small metal pipe that has a 90 degree bend in it and exits from the cylinder head on the rear of the engine between the exhaust manifold and the cambelt cover. I have managed to remove the large locking nut but the pipe won't budge, i don't want to risk destroying it trying to get it off unless i've got a spare. Does anyone have one?
My car is a 1989 bertone 1500cc.
Thanks in advance. Matt