Thanks for the update Topcat, I'm glad you have yours fixed.
I've made no progress on mine other than to read through a 3000 page workshop manual complete with parts diagrams etc. (available free online via a link on another Land Rover forum) on the car as well as buying a Haynes manual and reading through that in an effort to try and get some clue as to where the problem might lie.
I had established that one of the pipes does contain a not return disc valve loosely fitted in the end and was suspecting that to be behind the fault however I have been unable to find out which pipe it is in without taking the pipes off to have a look. The disc valve does not appear to be available as a separate part.
At least I now know for sure that new pipes will fix the problem and that it's not the return pipe I need. I think that leaves 3 pipes (2 of them come under a single part number so 2 'parts'?)
I refurbished my Haldex (gen 4) the other day which was easier than expected and fixed the common juddering while steering problem / stuck in 4wd that I also had so this steering problem is now next (and last) on my list of things to fix. I will now buy a set of power steering pipes and get them changed.
I'll post again for the sake of completeness when I have done the job and hopefully fixed mine.
Thanks again for the update!

Hi, I also need to do my haldex. I am looking at some ebay kits and thinking aobut doing it on the car. Did yuo remove the haldex or service in place? Was there any issues or particular tools needed for the hard to reach areas? Thanks.

I think the non return is in the steel pipe at the rack but when to have the access it is propably better changing the 2 pipes as if you have to go back in there maybe more expense.

I bought the parts I needed from these guys. Worked out about the same price as ebay. They delivered quickly but initially sent a wrong part (sent a syringe and pipe instead of one of the o ring seals). I contacted them and they were very apologetic and helpful and rushed me the correct part out. https://www.haldexrepairs.co.uk/product-tag/land-rover/
I got a filter, pump o ring seals, 850ml haldex oil, large rear o ring seal and (having read that some people had trouble separating the haldex from the diff and had to remove both, loosing diff oil in the process) a bottle of diff oil which I did not use. I also found the syringe very useful for refilling so would buy one of those too. About £90 delivered.

I didn't need any special tools but you would need a good socket set with several extension bars, universal joints etc. There's some none standard headed bolts on the propshaft but ring spanners work on them (8mm). Tricky to get to all the propshaft bolts unless you have wheels off the ground so you can turn it. (I had the rear on old fashioned ramps about 18" high and having removed 2 bolts and loosened any more I could reach rolled the car forward, just off the top of the ramp to reach the others. I removed the front diff mounts which allowed it to pivot down on the rears just enough to get at the bolts to separate the haldex

If yours just wants a precautionary oil change I'm sure oil and filter will be fine. If it's sticking like mine was everything I've read says you will need to remove it and strip it to fix it. You will not be able to remove much oil to change it on the car and will struggle to get at the filter anyway.

I removed it from the car, stripped it down and washed it out like in the 'Russian' video that's knocking about. I used turps to wash it out then blew it through with an airline. It was very easy to do. If you have the diy skills to remove the haldex you have the skills to strip it and wash it out. Changing the oil and filter would not have removed the sludge that was in there or cleared the debris off the pump intake filter (part of the pump, not the main haldex oil filter) It appears to have fixed the problem and has been working as it should since.

Yeah I'm going to pick up a full set of new steering pipes (excluding return) and change them. I already have a new reservoir ready to go on. Will be a few weeks as I'm going away in it and won't have time before I go. The haldex seemed more important because it was doing 5mpg less if nothing else.

Thanks, Thats the kit I was looking at on fleebay. Same price delivered.

I will save the haldex for winter given the amount spent on the PS system

I've replaced the pipes on mine now and the noise has stopped. It was a pig of a job getting to awkwardly located fasteners. After so long it's strange driving it without the noise being there. I can't see anything wrong with the old pipes which all blow through freely with an air line in both directions. I also changed the reservoir while I was at it. The one way disc valve fell out of it's recess in the rack while I was cleaning everything up. I prodded it a bit to make sure it operated smoothly and put it back in it's recess. I wouldn't be surprised if this bit dislodged a bit of dirt or grit from in it and is actually what fixed the problem.
Parts changed 2.2 TD4 FEED + RTN PIPE LR029185 and 2.2 TD4 LR001099 PUMP TO RACK and RESERVOIR LR000578.
I did not change the low pressure rack to reservoir pipe.
Thanks for your help identifying the cause of the problem Topcat.

Glad to help. Just wish I had found it before buying and fitting a rack and pump.