Flushing PS pump

I am having my original power steering box rebuilt and upgraded for more feel. My federal pump was not leaking and was operating smoothly, so I really don't want to take it apart, but it was suggested that I flush it out to ensure there are no contaminants that could get into the fresh box. What kind of solvent would work without affecting the seals?

Even after flushing, I run an in-line filter in the return hose that is specifically designed filter for transmission fluid, has a magnet in it and costs about $25. I leave it in.