Acetone will remove the varnish. For rust fill with bolts and shake until all of the loose stuff comes out with the bolts. Fill with white vinegar and let sit for a week or more. drain out, add some baking soda and water, slosh and flush with fresh water. add some denatured alcohol, slosh and drain, air dry. if not going to be used for a while, add some oil, slosh and drain.