I used to use Phil's Tenacious oil to lube my old freewheels. One time when my freewheel sounded particularly gritty, I soaked it in a bath of mineral spirits, spun it to agitate everything inside, let it drain out then dry on some old rags. I repeated a couple times until the solvent that drained out looked pretty clean, then I did it one more time with a more volatile solvent. I don't remember if it was acetone or rubbing alcohol or what. Then I let it drain and dry out for a while and dripped in Phil's oil while spinning it. It worked fine and was very smooth and quiet after that treatment.