Thanks for the comments.
This is the bleed screw on the PAS box, so it should be a high pressure seal, so I would think it needs either a metal to metal or o ring/rubber in there somewhere?
I don’t think a fibre washer sounds right.
If I seal it up it will not work as a bleed screw?
I cannot find C2296/5 anywhere - I see C2296/2 which is a sump plug seal …
In the end I have sealed it with an o ring and have some 1/8" BSP dowty seals coming to see if they fit. The problem with using an o ring is that as soon as you try and use it as a bleed screw the seal seems to be destroyed. I have driven it around without bleeding it and there are no leaks - however, I still have slightly different steering response left and right, so would like to bleed.
The bits I am talking about are 14 and 15 in the diagram below, but I have no legend and don’t know where this came from - is a later version of the box than is in the workshop manual or Haynes manual.
Regards and thanks