The latest ATF's have additives that are not good for the seals in your power steering. Simply go to the auto parts store and buy a few quarts of what is labeled "Power Steering Fluid". It's more expensive than ATF, but much less expensive than a pump. Been there, done that!
If you really want to be safe, buy Power Steering Fluid at your dealer, but I really believe the generic stuff is fine. These components are expensive, don't take chances.