Power steering fluid.
http://www.c32life.com/engine.jpg
By the way, if you're having to add a lot of fluid, it means you have either an external, or worse, an internal leak in your PS rack, pump, or lines.
Look for obvious signs of a leak by removing the plastic pan under your engine bay. Get it fixed ASAP if it's leaking. You do not want to buy a new PS rack.



