Pascal: I am assuming that you checked the fluid level to make sure there was adequate fluid?
The pump has been known to be a bit noisy especially when the rack is under a lot of load: making turns at very low speeds.
Here is a section of the service manual addressing the track rod ends, gaiters and inner ball joints as well as pump tests.
Rack-info.pdf
Here is a picture of the basic rack and the areas I circled could all contribute to excessive play in the steering.
rack.jpg
You will need to find a way to have someone steer back and forth through the range of free-play or slop while you or another technician watches each area to see of motion is being lost due to wear or other issue.
See this post regarding the inner ball joint causing play in the steering:
viewtopic.php?f=108&t=23523#p303501Here is a picture of an inner ball joint (inside the steering gaiter)
Track-Rod-Joint.jpg
You can't see this unless you slide the gaiter off the ball jount, but you can check to make sure there is no play in the outer track rod end as well as the upper and lower ball joints. If the lower ball joint is going bad, you will get excessive free-play in that axis and if it is starting to rust up internally, it will inhibit rotation so you have to steer harder and constantly correct as it takes more force to return the steering back to center.
If there is steering motion loss inside the actual rack and pinion housing, then a full rebuild or replacement is in order.
To test the ball joints, you jack up that corner and put a stand under the Lower Arm (TCA) out under the ball joint and then let the jack down enough to add weight to the spring but not damaging the TCA.
Articulate the wheel in and out at the top and bottom while watching for play in either ball joint and also rotate the wheel through the turn radius and "feel" for any tightness or grinding caused by the ball joint rusting.
If this is a bit more than you want to do yourself, an alignment shop or front-end specialist can do these tests for you and advise if you have any issues.
Lower Ball Joints, Track Rod Ends (outer tie rods), upper ball joints and steering rack gaiters are all still available from Lotus.
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