Castrol TQ-D - automatic transmission fluid. Halfords have it usually.
Pretty much any ATF will work. But, Castrol also have TQ-III which
is in a similar 1ltr bottle, I've been advised this isn't the stuff to use
(don't know why?!)
A 1 litre bottle should do it - my Vitesse took just over a litre when I
fitted a new rack, and it has the power steering cooler, which your
V8-S doesn't have.