1999 W reg 90 with a Steering issue??? HELP!!!

Good Afternoon all, Im after some advice please, A Chap I work with has a 1999 defender 90 diesel, The problem hes got is as follows:

The Steering seems more difficult to turn Right than Left and When driving down a twisty road the steering will CLONK Loadly and the whole car will leap towards the middle of the road, as you can imagine its quite an un-nerving experience especially when towing a heavy trailer!!

The Steering box was replaced about a year ago and the track rod ends were done in December for the MOT. Tracking recently checked and is all ok.
Whilst crawling underneath it in the yard you can simulate the same CLONKING noise and see the track rod arm jump by turning the steering right to left and back with the engine running. Unsure if the jumping track rod is the cause of the problem or a result of something else be knackered?

Any ideas/advice would be greatly recieved.

have you looked at the UJs under the bonnet along the length of the steering column ?

Hes checked the one you can see from the engine bay and it has very slight play but no clonking, is that the only one or is there another one hiding away towards the steering box?

yes.

could be his steering box, the power steering getting a bit enthusiastic?

I rekon change the PAS fluid and look in the old stuff for bits.

boydy1989Re: 1999 W reg 90 with a Steering issue??? HELP!!!
yes.

could be his steering box, the power steering getting a bit enthusiastic?

I rekon change the PAS fluid and look in the old stuff for bits

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Spoke to my mate this arvo, he seems to think the box is ok, as it was new about a year ago, but will drain the fluid just to make sure as per your suggestion.
One thing he did read on the tinternet, was that some boxes have problems with Air being trapped in them? Anyone had this trouble and would be it cause this type of problem? If this is the case, how do you go about bleeding the system?

if i remember correctly theres a bleed bolt on the top of the PAS box. I cnt remember the correct proceedure, haynes book of lies tells you, rave probably does too.