Kroil's always been a handy one for me.
Also, push come to shove, after several days of applying penetrating oil
several times a day, try getting the stuck parts
extremely cold. Like minus 40 (degrees) or better.
Sometimes the contraction helps to shrink things enough so that they're small enough to not have so much of an interference
Just be gentle, as at real low temps, metal can get brittle.
And this one's just a theoretical fix. But how about a few soaks in vinegar or Coca Cola. To let their acidic properties eat some of the corrosion
It'd likely make sense to try it out on something unimportant first, but... if you're truly @ a loss for fixes...
Plus, there's always Google
, & or talking to a master mechanic
. Likely between those two, you'll find some ideas.
Oh, and Doh! How about querying a Master Rigger? I'd imagine that they've run into this kind of thing a few hundred times over.