If the kroil doesn't work mix up atf and acetone 50/50. be sure to use a glass or metal container (plastic will melt). this is my go to penetrant when nothing else will work. it's never taken more than 24 hours to work and usually it is a lot faster than that. A lot of my repair work and day job requires dealing with salt corrosion and galvanic corrosion in the marine environment. this mix has never failed me. good luck.

90 LWB - Not your average bear

"You are what you are, and you ain't what you ain't." - John Prine