V8 loosing coolant

My 2003 Disco is loosing 1 litre of coolant every 60 miles or so, most days. Sometimes it doesn't loose any coolant at all.

It seems to build up pressure and dump it from the back of the engine and it's really frustrating trying to find exactly where its coming from.

I think I may have found where it leaking at long last but could do with some advice.

On the bulkhead there are two male connections where the heater matrix feed. It looks to be made of rubber and there is a visible gash on the rubber.

I'd like to know if it is rubber or just a sleeving,if so, this is obviously not where the leak is coming from. If this part does need replacing it looks to be a bugger to do as I think it will involve taking the dash out to get to it from the inside. Any advice on changing this part would be appreciated.

Are you using o.a.t coolant as you should be,if so a leak should be obvious as it leaves the area orange,Afraid to say it could be a head gasket problem or a loose liner,have you got any tapping noises? Why not get the system pressurised to see if you can spot the leak (hopefully!)