Get a pump spray bottle and some Turpentine (wood sap distillate product) and spray stuck surfaces as well as movable fingers and pins.
With a mallet or LIGHT hammer tap to set vibrations through assembly. Keep at it twice daily and you should find the turpentine penetrating and "dissolving" the oxidation until stuff can be gently pried loose.  You need to be patient and let the chemical reaction work.  It did not rust together over night and the reversal will take time also.