[Beav]

If you're losing fluid and can't find any signs of it, it's possible that the end seals of the steering rack are leaking and the lost oil is collecting in the tie rod boots. If so, it will continue to leak until the boots can't hold any more and gush out, usually all at once and onto hot exhaust pipes, creating a fire hazard, not to mention how much fun it is when the rear tires are skidding along on a freshly oiled roadway. (is that a record for a run-on sentence?)

Take a moment or two and reach under the car and squeeze them to see if they are holding oil, they won't bite.

A low speed vibration can occur anytime the fluid is low.