I have a Cochin and a Brahma. When they've had scaly leg mites, I've dipped their feet and legs, foot feathers included, in castor oil. It's a real yucky mess, but I turn them loose back into the sand run. After a few days the thick oil has all disappeared, feathers are clean again, and the leg mites are gone.
Since then, I've discovered that Elector PSP, a spinosad biological insect control, works splendidly in a single treatment for leg mites. So now all I need to do for leg mites is a ten minute soak in a basin of water with a quarter teaspoon of Elector mixed in and there is no longer any messy oils to deal with.