The power steering system is supposed to be a sealed system and not loose or "burn" fluid. The system only consists of a pump, steering rack and power steering high pressure hose and return hose. It doesn't make sense that the fluid just disappear. If it were a serious high pressure leak the fluid would leak out very quickly as the pressure is very high. Check the end of the steering rack are the rack boots wet and or torn? If so it may be an internal rack problem. Check the pinion seal where the steering column enters the steering rack see if it is leaking. Take a close look at the steering pump area, you may need a mirror and flash light to pinpoint the source of the leak. The high pressure hose has metal and rubber hose. The hose should be dry and not damp. Get someone to operate the steering from side to side as you look for a leak from the hoses.