I've got a Freelander 1999 2.0L DI. I need to top up some power steering fluid. In the manual it says to use Dexron IID or Dexron III. I'm wondering whether I can use Dexron III H (e.g. Castrol ATF DEX III) for this purpose as well?
You should be fine using the Dexron-IIIH. The "H" indicates a newer additive package than previous versions. According to OilSpecifications.org:
Dexron III licence H was introduced in June 2003 to replace the Dexron III G fluid. It has an oxidatively stable base oil (group 2 or group 3). Oils according to this specification have longer maintenance of friction properties and anti-shrudder properties, better foam control and a longer fluid life.
It's just better Dexron-III, is all.