KROIL from the Kano Labs in Nashville, Tn. is the best stuff I have
ever seen.
Spray a liberal amount of KROIL. Let it set for a while and tap
gently.
If you are able, spray some more KROIL into the hole and pressurize.
Leave the pressure on and the pressure will help force the KROIL
through the rust.
I have used this method to free up stuck 3 point center links on farm
tractors.