Hey, I'm a big fan of keeping old stuff running, after all my only car is 27 years old and has over 300K on the clock....BUT.....
My time is worth way more to me, and old high-quality freewheels are in such abundance (you have to know where to look). Unless a flush frees it up, and it sounds right and spins freely, it's broken! And there's no way I'm going to bother disassembling one. Even if it has a broken spring or pawl, where are you going to get one of those?
Flush it out. If it refuses to "wake up" and work right, it may have severe internal corrosion. Cut your losses and move on.