Here is something that AACA Members claim works the best .
ATF and Acetone tested on a rusty screw, bolt, see what the results were of the Test. This 50/50 mix is the most effective, inexpensive, cheapest penetrating oil you can make at home. A homebrew to break rusty bolts loose. I didn't believe it until I did this test of Acetone and Automatic Transmission Fluid.Feb 14, 2015