Best penitrating fluid

[TX '90 ZR1]

Back in my airplane days (80's & 90's) the older mechanics who worked for me insisted on a product called "Mouse Milk" to free frozen nuts & bolts. They would put just a small amount on the nut or bolt and apply a little heat. I was amazed how well it worked.
Don't know if it is even still available. I had to order it back then through aviation supply houses.
I was told that the reason it was so expensive was because you had to milk a LOT of mice to fill up a can!!!