What make was the original ? ... Well LR like others uses several OEMs for the assembly lines, Monroe is one of them. Britpart is not an OEM just a supplier and do supply 'Genuine Parts' so why are they "out" ?.
If you have a vehicle used in comps then use Bilstein as the also make very good HD suspension dampers, other wise use just a bog standard stealing damper at under £20 on eBay I believe.
The steering damper is not supposed to return anything to anywhere. The castor angle does the self centering. What you mean is the damper is stiff on cold mornings preventing self centering. That should not happen.
i have terrafirma on steering... i like it.. a bit heavier than OME... had to dump air suspension for bearmach springs, so also have terrafirma gas dampers fitted all round,
again, i like the feel and handling, then again... i drive big artics for work, so light steering is not what i like, hope this helps..
Ah, probably should have said, I went and bought a Land Rover one as I prefer the Boge over my old Terrafirma shocks. Not got around to fitting it yet as I've been fiddling with other stuff.