Phil Wood Tenacious Oil is the most correct answer to your question. Best to take the freewheel off the bike, so you can get it really clean, but also works with it still on the hub.
Slowly drip the Tenaciousness into the gap between the part that moves and the part that don't while spinning the freewheel. If freewheel is off the hub, do both sides. You'll feel when the oil gets drawn down into where it goes. When it stops feeling better, wipe off the excess and put the freewheel back on. Grease the hub threads before doing the last bit. The sanity you save may be your own.
Making this a part of your winter screwing-around-with-the-bike routine is wise.
--Shannon