I don't do much with ponds, but I replaced a pump in March for a client. he called again two days ago and said he thinks it is going out again. He said in March that he had gotten a slight "oil" slick in the water and then the pump had seized up. He says he has the same "oil" slick again. The pump is an Aquascape 3000. The original was an older vertical pump. New one is horizontal. Company I bought the pump from said they do not have oil in them anymore so it should not be from the pump. Any other thoughts? Is it the pump? Dead fish somewhere causing oil?