Or for a shade tree GOB fix, unhook/plug the vac line, wire the butterflies in the open position shown, and gob on rtv over the leaky end and let it set up before you drive it. Are you SURE it's the butterfly shaft bushing leaking, or is the acutator diaphragm leaking? Piece of vac hose 3' long, one end in your ear, makes a nifty leak finder.

Not responsible for advice not taken...