Transmission fluid is a very high detergent, multi-vis oil, on the order of 5W10. Once the acetone softens up the plastic, the ATF gets behind it, and gets it moving.
WD-40 actually does the same thing. WD-40 is not a lubricant, and the carriers in it will evaporate the light components of modern oils, leaving heavier components that then turn to a varnish.
Don't use WD-40 and oil together. A light smear of blued surfaces with a cloth that has a bit of WD-40 on it may be the best rust preventative in existance.
Best,
Ted
