If you put a button-sized magnet in the bottom of the funnelscreen, your power steering will keep most of its performance for many years. Add enough fluid ( 1-2 cm) to raise the "cold" level so as to submerge the magnet. Check the magnet occaisionally and clean off the gob of gray sludge when it gets too thick. You can also suspend a magnet into the reservoir itself but if it gets loose, it may clog the outlet tube --or worse.

Magnets serve the same function in power steering as those in the automatic transmission---they filter out all of the small steel particles from gear friction. They are too small to be picked up by the screen, but in the large amounts that accumulate over time, they create much additional wear.