Do oil leaks cause an automobile engine to lose power?

Answer 1

Yes, they can indirectly by fouling your spark plugs for example. A faulty Positive Crankcase Ventilation (PCV) system could also allow pressure to build up in your engine's crankcase and unbalance the engine's air/fuel ratio mixture causing a loss of power. That could exacerbate oil leaks. Another example of an oil leak causing loss of power is on an engine whose spark plugs are recessed into wells in the valve cover. When the oil seals at the base of the wells leak oil into the wells, the spark plugs misfire causing loss of engine power. Of course internal oil leaks may eventually cause loss of power in connection with sensors and your catalytic converter.

Answer 2

No but it is possible that you have oil leaks because of the low power. If the rings have failed allowing the compression and combustion gasses into the crankcase it is possible that the excessive pressures are the cause of your oil leaks. This is a fairly common concern on high mileage engines.