They did fit a genuine one, although price wise they're a lot more expensive than aftermarket.

When I had the suspension error message it turned out to be a low battery voltage causing it (thankfully). A full re-charge on trickle overnight cured it.

As others have said the suspension turret wiring is the Adaptive Dynamics fault

Should the suspension make any form of hissing noise under normal operation? I have had the 30mph fault, seemingly triggered at quicker speeds, and had a journey that was less than a mile thankfully, on the bump stops. It cleared when I switched the car off and on again. I was grateful to see this topic at the top of the list! One of my front struts makes a loud hissing and the car wont go up to off-road height so I was thinking split bag? 2012 Westminster Aintree/Ivory 4.4TDV8

Yep, you’ve got a split bag.

Figured as much. Thank you for confirming. I’m going to look at the date on the shock but I think they may be original and will therefore be past their best. There was no suspension work showing in the history.
I’m assuming best to replace both sides at the same time?
OEM the best/only option?
Finally, who is flavour of the month for ordering parts? I think I read that AF have removed the discount code and are operating some kind of reward model. Open to suggestions. 2012 Westminster Aintree/Ivory 4.4TDV8

It is best to replace both sides, but, check the date on the non leaking bag 'just in case' it has been replaced. My front offside failed recently and was found to be 18 years old ! Checked the other side, it is the same age, so it will be replaced soon. As for OEM, everyone has a different choice. As my originals were Dunlop and lasted 18 years, I went for the same again. Shop around, to find the best deal, there are quite a few good suppliers around.

I went for changing the complete strut unit due to the age, and 140.000 plus mileage, not too bad a job to do, apart from one of the main bolts needing a sledgehammer to get it moving

Thanks for this. Will be taking a look at them this afternoon. I’d imagine they’re pretty old and so will replace both if so. 2012 Westminster Aintree/Ivory 4.4TDV8