That is why it is worth paying a good taxidermist. Some of the steps that you may have missed.... 1. did you open the wings to get all the meat out? 2. Did you get any and all yellow fat out between the feather tracts? 3. Did you preserve the feet? 4. what did you do about the bill?
I degrease mine ( I only do ducks for me and my family) with Dawn dishwashing liquid and then Coleman fuel. The CF is more for water displacement than degreasing but it does break down some grease. Ducks are difficult to learn on without good video or someone to teach you. Let me know if I can help