New Heater Matrix Core with O-rings fits Range Rover P38. 

Part STC3261 - Heater matrix (1 pc)

Part STC3262 X2 - O Ring for the heater matrix pipes. (2 pc)

Models Affected:

Land Rover Range Rover 4.0 (P38) 1995 - 2002

Land Rover Range Rover 4.6 (P38) 1995 – 2002

Always get a professional to diagnose the fault before attempting this fix as it is a very difficult task.