Actually I use the goat milk to THIN my acrylics when I spray them on... incredible adhesion with that! (kidding as well)
Oven cleaner such as easy-off, Castrol super clean (you can get it in the automotive cleaner section at Wal Mart or auto supply stores) work great... put the piece in a plastic ziplock bag, spray either on the figure and seal in the fumes, let sit at least an hour (some say more, some say less) get an old toothbrush and (wearing gloves) brush off any remaining paint.
Clean it up in soap and water and BAM!!! you've got a fresh piece ready for painting! I the paint is being stubborn you can put it back in the bag to soak longer. I've left stuff for several days before with no bad results... Just keep going back and checking and scrubbing with that toothbrush now and then if ya do... And wear gloves... voice of experience..