Originally Posted by DetMich1

There is a similar problem which involves disappering power steering fluid with no visible leak or puddle on the floor where the car is parked. This can be caused by a bad valve on the power steering hose. There is a vacuum line that advances the engine RPMs slightly (opens the throttle) when the steering wheel is turned while at idle. If the valve fails, power steering fluid can be sucked into the intake manifold and burned off with the air/fuel mixture. Results in loss of fluid with no visible leak.