fluid seal fell into power steering reservoir

Sorry to hear that. You're not going to like my answer. The cardboard is surely ground into bits by the pump by now. There are numerous small passages in the rack that are very sensitive to debris in the fluid. Even if the cardboard dissolves, it still presents foreign matter in the fluid. It changes the characteristic of the fluid, and it can't stay in there. You will eventually experience hard steering and premature pump wear at the very least. It's not ALL bad news however. For now, try to flush the entire system thoroughly by removing the hoses at the rack. Turn the steering wheel lock to lock a few times to pump the fluid out of the rack into a large pan. Drain the pump reservoir fluid into the pan as well. Spin the pulley by hand in both directions until it's completely empty. Pour the collected fluid thru cheesecloth or a paint filter and see if the debris is showing up. If not, you'll have to do this a few times over the next month or so. I think you'll be okay if you can get all, or most of the cardboard out of the fluid.

http://www.amazon.com/gp/aw/d/B00275F5I8 Try using a mechanical pickup like this to fish it out.