I also think that the best approach would be to replace completely the steering box, since it is such a critical steering part.
As to why this happened, perhaps it was run dry for years?
Anyway, as far as i know, 2000 cylinder steering boxes are the same, apart from the later 2200 cars. For instance it is exactly the same with my 1970 TC. Also i think that the only difference between RHD and LHD is the bottom arm. So, if you cannot locate a complete LHD box, perhaps you can swap your bottom arm with the one out of a RHD box. But please verify this last information first before buying something, because i am not 100% sure on this.