Without taking one apart, I have seen people spraying WD40 into a freewheel body to clear it out, and then dripping Phil's tenacious oil into it for lubrication. The thickest stuff I have available at the moment is wet-weather chain lube. Will this work or destroy the freewheel? How important is viscosity here?
The only freehub-specific lube I have found is from Dumonde Tech. They offer a freehub lube in both oil and grease form; depending on your preference. Those are what I use when servicing my rear wheels. Cleaning with WD-40 isn't bad practice as it's just a water displacement solution (Thus the "WD") and only imparts a very, very light lube to whatever surface it covers. I use it for cleaning bike and motorcycle parts all the time and to add some protective covering to parts with exposed raw metal.