I'd be inclined to soak the Supertool in very hot water with dish soap, leave it for a while to soften the oil that will doubtless have solidified over the years. Then begin to slowly work the tools open in the hot water. Turn the oven on high . remove the tool and pour boiling water from a kettle over it.. Pat it dry with a soft cloth, place on a baking tray and shove it in the oven for half hour.. Remove, allow to cool and soak with copious amounts of WD40.
It's what I always do and has never let me down nor caused rust issues.