I think you need the full fat variety. I had a similar prob yesterday...realised I only had diet in. I read something about the aspartame in diet coke going a bit funny when it's heated, so I vetoed it and boiled it in cider instead. Still yummy!
Little owls, don't panic. You are supposed to remove some of the fat, atleast most people do. I soak mine all day, boil for an hour, then cut off most of the fat. then into the oven, cover in foil for 3/4 of the time, then uncover, pour marinade over and then cook for the last 1/4. Always works for me.