Would that not mean that the contaminant remains in the hydraulic fluid as it is a closed system.
Are all the steering hydraulic systems completely flushed and refilled if this is thought to have occurred? If not why not?
A work colleague who had a lot of experience with hydraulics, advised against flushing out hydraulic systems unless absolutely necessary, as the smaller debris in systems that have already had a lot of use often help with sealing(!). Once flushed out, a lot of further maintenance is likely to be required as parts that were sealing no longer do so. I would assume that there are a range of filters in the system to catch the larger debris of the sort that caused the problem in the thread, and one would expect those to be checked and changed at regular service intervals.
Inspection and cleaning procedures here:
http://www.faa.gov/regulations_polic...a/ama_ch12.pdf