Many years ago, Group Six in Arizona a well established (but now defunct) aftermarket parts fabricator and supplier for Saabs, advocated installation of power steering filters to help improve the longevity of P/S pumps and racks. Having recently replaced a pump and rack, I decided to take this advice and do something proactive to try to keep these newly rebuilt units functioning in tip-top shape for as long as possible.
Installation is very simple:
1) Pinch off the reservoir return line (the low pressure side is always best for in-line filters as the chance for leaks is lower and you don't want to put a potential bottleneck or flow restrictor in a pressurized line) as close to the clamp at the bottom of the reservoir as possible with locking hose clamp pliers or a small c-clamp.
2) Cut the hose at least 1 and 1/2 inches above the clamp-off point. Place a new clamp on the 3/8 inch ID hose and insert the bottom filter hose barb into the hose and tighten the clamp. (The filter is marked at each end for in and out flows).
3) Cut the hose above the filter to insert the top hose barb of the filter, leaving some extra hose so the filter is not pulling the hose taut. Place a clamp on the hose, insert the top hose barb of the filter and tighten the clamp.
See the finished product in the NG900 & OG9-3 performance modification forum:

http://www.customsaab.com/forum/viewtopic.php?p=501#501