1999 E39 523i HEavy Steering

[arh]

I have been having a problem with heavy steering on and off for a good few months. If I change the fluid the problems gets better but the steering gradually gets heavy again. It is heavy but still relatively smooth.
There are no noises coming from the car.
Went to a mechanic today that diagnosed the problem as the pump. He opened the fluid container and turned the wheel in both directions with the car on. There was no changes in the level of the fluid. Is his diagnosis accurate?
There is also a very slow leak in one of the pas pipes.
Is there any test for the rack as I really hope that this is not the issue?
Could it be something else apart from the pump or rack? I have checked the tyre prressures and both front and rear anit-roll bar bushes have been repalced.
Thanks.

[arh]

Can someone also advise me on how much time it would take to get the pump changed over so I can work out how much labour I should be paying. Thanks.

[brettski]

Has you mechanic given you an estimate for the time?

At a guess I'd expect it to be 2 - 3 hours, but I really don't know for sure.