Lnd Rover Steering problems

Ive just bought my first Land rover (defender 90 TDI 1991), and just
wanted to check a few things.

First off, it has power steering, but this only works properly when
the engine is rev'ing fairly high. Is this normal, or a problem with
the PAS pump?

Also there is a fair bit of play in the steering, again is this
acceptable. I think ive tracked it down to the steering box, if this
was replaced with a reconditioned one is it sort out the problem

Thanks for any comments

Simon