I clean freewheels in a 50/50 denatured alcohol/acetone mix with a ultrasonic cleaner, because there are people out there that think filling a freewheel with spray can chain lube is a good idea, This solvent mix will dissolve almost any 45 year old goo that's in there with a one or two day soak, If that doesn't do it switch the solvent to MEK (methyl ethyl ketone), followed by blowing the internals with compressed air. For lubrication I use 85W/140 gear oil injected with a syringe and let it drip dry for a hour or so before installing. I have had good luck using this method.

: Mike