The steering box can be taken apart and the internal and external seal kits replaced, they are readily available.
I posted Videos on this recently, showing the complete job…I will edit this post and link it, you will see what is involved then
The lower seal can be replaced in situ, but didnt stop mine leaking, I replaced the box with a used, but rebuilt one.
They have the same seal kits as Landrover (Defender and other models) steering boxes for Adwest Marles in Jaguar boxes
Unless you have reasonable technical experience, I would have the rebuild completed by a steering box rebuild specialist.
have a look at the videos and decide for yourself