leak from pipe
 

Hi, on my 1984 D24T engine, there is the metal pipe that runs along the inlet manifold that joins a rubber hose that's between the pipes to and from the heater matrix. It then goes round the back of the head. I need a new rubbe r hose. Any part numbers for it?
NOT the heater pipes!
https://imgur.com/a/Br76Niv

pic
 

That is still part of the cooling system in a way, gets coolant to and from the oilcooler. Easily repaired or substituted but if you want a factory metal pipe that can be harder and can take longer than fabricating one. NICE CATCH! The cooling system must be top notch for the health of the motor.
Maybe someone here will say that it is time for you to get rid of that line completely and remove the oilcooler with it.
It is an easy fix to make and prob worth it. I personally would keep it on for the stock look and because oilcooler has function under very heavy loads or when towing equipment extreme distances/living in mountanious area you may be happy to have it. Idk.

You are only looking for the short rubber hose, correct? Not the entire metal pipe?

If you just need the hose, it is simply a short length of standard 5/8" heater hose, available from any parts supply house. You can just get some bulk hose and cut it to length using the existing hose as a template. If you can find silicone hose, this location would be a good choice for it since the most common reason for failure of this hose is oil leakage onto it, which silicone would be less affected by.

Good idea to also replace the rubber O-rings under the hose nipples that mount in the back of the head and block while you are working back there. Any oil leakage will also affect them, plus simply age/time.

Good rubber 1-piece valve cover gasket is the solution to eliminating valve cover leaks.

gasket
 

where do you get the one piece gasket from? It has been leaking from the valve cover gasket.
I have a piece of replacement pipe, so all good.

Have you tried brickwerks.co.uk?