The air pumps that I have taken appart do not have anything like oil or such in them. They are typically a nylonish type plastic body with a rubber diaphragm that is vibrated back and forth by an armature. There is no liquid or goo involved. I can't imagine why or how one would have liquid in it.
Typically pumps or power heads intended for underwater use will be filled with oil because liquids are not compressible. If they were filled with air, tiny leaks would allow them to fill with water because of the difference in outside and inside pressure. By having it filled with oil, there is no place for the water to go. The oil will not compress so it will not allow water to enter. If oil leaks out, it is an indication of a serious leak. Water and/or air will have displaced the oil. Either way, oil out is a good indication water has gone in and the pump or power head should be removed from service or repaired.
Any time you need an answer, just ask.
thanks again bro (My fish thank you as well ) It's funny the fish have really become part of my little family. They all watch the tanks and are now looking at the equipment etc reading up.