* Power Steering Fluid Leak: The most likely culprit. A leak in the power steering system (hoses, rack and pinion, pump seals, etc.) will allow power steering fluid to leak into the pump. Since engine oil is also under pressure, the oil can be drawn into the power steering pump through the leak.
* Damaged Power Steering Pump Seal: A worn or damaged seal within the power steering pump itself can allow engine oil to leak *into* the power steering system. This is less common than a leak elsewhere, but still possible.
* Failed Oil Cooler (if equipped): Some vehicles have an oil cooler integrated into the power steering system. A failure in this cooler could lead to oil mixing with the power steering fluid. This is less likely on a 1999 Ranger, but worth considering.
* Incorrect Fluid: Though rare, if the wrong type of fluid was added (engine oil instead of power steering fluid), it could lead to the situation you describe. However, this usually results in immediate problems beyond just oil in the pump.
In short, finding oil in the power steering pump signals a problem within the power steering system that needs immediate attention. Ignoring it could lead to power steering failure and potentially damage to the pump itself. You should have a mechanic diagnose the leak's source to prevent further damage.
