If you have gotten rid of the chair and cleaned and painted the porch, then the only thing I can think of is that it leaked out and went below the porch decking. I would look under there and clean it up and use a mild bleach and water mix on the underside of the decking and on the floor/soil underneath. There isn't much that will still stink after a thorough cleaning and bleaching. Wear eye protection when using bleach and cruddy clothes b/c bleach ALWAYS gets on your clothes. Good luck!