Our OBW has 122,000 miles on it and we never had the steering fluid flushed. However, with my recent work on the car, I flushed the power steering system by unattaching the power steering reservoir then finding out which was the feed pipe to (from) the pump. Once I knew that, I put the one pipe extension on and fed the system new Dexron VI Valvoline Full Synthetic AT oil. When the fluid started coming red (about a quart or so), I stopped, connected the reservoir back up and topped it off with the new fluid.
I have had vehicles go nearly 200,000 miles with the original power steering fluid. You can purchase Power Steering Fluid Conditioner which is supposed to help all the rubber parts and help stop small leaks. I have put some of that in the reservoir, in the past, but used it sparingly.