I wonder if any expert out there can help with a problem my dad is
having with his Primera, in particular, the power assisted steering...

First of all, most of the time the steering is completely normal. This
is particularly so when the car has been standing for some time, such
as first thing in the morning. After a while - maybe five miles or
so...

The steering get noticeably stiffer. When the car is stationary the
steering becomes very stiff (e.g. when manoevering in a car park).
When driving along, it becomes more difficult to correct slight
wandering tendency (dad says that it feels as if steering/track rod
ends have some free play).

He's taken it back to the garage that sold it to him but they say
everything is fine. Work at another garage has included a replacement
power pump, steering oil replaced, all tyres renewed and the steering
joints have been checked and given the all clear.

As this one problem is denting my dad's enjoyment of this otherwise
perfect car, any suggestions you may have would be most welcome and
much appreciated.

38K on the clock BTW.

Regards - Martin