I am not recommending de-solder. and rewire. I have not seen condition of solder joints but there are now only a few wires on the switch which are used. I would splice with a modern solder sleeve splice or whatever way you like. It can be a can of worms you don't need. Old phenolic boards and solder joints/pads/terminals can break off or some other unforeseen event. If wires are tight, I would consider leaving alone. Heating the board is not a good idea.
To use the solder, test it on some wire joints on the bench. Some solder does have a shelf life.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
