Thelma, Vinegar, a weak solution of acetic acid, reacts with the zinc in the galvanize coating and will mildly etch the zinc. This is about the same effect that you get by putting a penny in a jar of vinegar and leaving it over night. Yes, as Steve: says, it will cut grease, but it's main job is to roughen the surface so paint or primer will stick. The steel that is used is even called "smooth rolled galvanized". Your window wells may have bee roughened by time, but they may still be so smooth in places that the paint will have a hard time finding the microscopic roughness that it needs to adhere. The vinegar is a good idea. Just rinse with plain water to stop the action after 15 minutes or so. The effectiveness of the vinegar will probably be gone long before this anyway.