Hi, my OS FS-61 was SEVERELY seized due to old and gummed up castor oil residue. Had to put it in the oven several times to loosen it up. The cam followers were stuck TIGHT, the rockers did NOT rock, everything was frozen solid.
My objective is always to disassemble projects without leaving ugly toolmarks or gouges.
The piston wrist pin was removed by inserting an M4 thread tap into the hole, after having removed the Teflon cap by inserting a small screw and pulling it out.
With the tap (and a small torch to heat the piston from below) I was able to exert enough rotational force to break the gummy residue that was holding it in the piston. It could then be pulled out, still stuck to the M4 tap.
Next project is the wax method to remove the cam bearings..