Oh yuck! Poor Whizzer! Mine was exactly the same way... you would have thought she was mint condition when you saw her but when I broke her open she was quite nasty inside. That's why I prefer to open them up every time- because you just never know!
Dawn brand dish soap works the best for me, because it contains chemicals that break down spores and prevent mold from ever coming back. You could also use Mr. Clean if you're having trouble, but I don't know how this will effect the eyes. I definitely second toothpaste for scrubbing out rust too as well as using an (old!) toothbrush so you can scrub scrub scrub!
If you use hot water, the plastic should become soft enough for you to work with, and it will be easier to get inside the legs.