d1driver said:
Don't waste your money on a used one.
+1. When I owned my RRC (same steering box as D1, I believe) I had to replace my steering box. At the time I was suffering from CHOP, a well documented condition affecting Rover owners known as CHeapskate Objectivity Paralysis, and I decided to go with a rebuilt box to save a couple hundred dollars.
The rebuilt replacement was no better than the leaky original. By the time I finally sorted the whole situation out it would have been less expensive to simply have bought a new replacement instead of dicking around with a rebuilt one.
There are some parts where replacement with used makes sense. Unfortunately this is not one of them.