I've just had exactly the same problem with my 2008 C5 X7 at just over 110k miles and thanks to this thread have just got back from Steering Specialists Ltd in Wakefield, who have fitted a new rack for me today 'while I waited'. I got there at 8.30am and they'd got it done by 2.30pm. They confirmed in my case it was the known issue with the input shaft corroding and shredding the seal. The replacement has been given a good 'ring' of copper grease to stop water 'pooling' where the shaft enters the rack, which is what causes the problem and they've recommended that this is wiped off and replaced during each service. They also recommended that I replaced the low pressure hose at the same time as they did the rack. The hose is terminated with an alloy flange, which Citroen helpfully secure with a steel clamp, so they also corrode terribly and they got fed up of replacing steering racks then getting cars back in a few days with a leaking hose, so almost insist on replacing them. I paid £340 for the reconditioned rack, including fitting and the low pressure hose is a Citroen only part and costs £100, which they asked for 'up front' 2 days before my appointment as they have to order from a main dealer. They were super helpful and a very genuine company that i have no hesitation in recommending.
