Ok, had to laugh when I read this. Probably not funny to you but the visual of a butt print on the cover was cute!

Did you try washing by hand and maybe scrubbing with a small brush or something (like an old toothbrush maybe?). Make sure you have a decent amount of detergent and hot water so that the oils dissolve. Just rinse well afterwards... You might have to do it a couple of times before it's all gone.

The stain may remain there permanently (like a grease stain in a t-shirt) but I really wouldn't worry about using the cover. You'd need large quantities of the cream right in the diaper before it would cause problems and even then it might still not cause problems unless you did it on a regular basis.

Karen.