For aluminum shafts, I have used the Muratic Acid. Home Depot here had two options, a "green" more environmentally friendly type, and the regular type. The "green" doesn't work well enough for this, use the regular. Carefully pour some in a plastic bin, and let the shaft soak in it. It will bubble and smoke, and put out some nasty fumes, so don't do it in an enclosed area, or even near a wall where the fumes can take the paint off (got that tip from someone else who did that). In one or two soaks, it will dissolve the aluminum shaft. It will also strip the paint from the steel.