Tosh is right. You need a solvent based spray. Mr. Muscle actually works very well. But the spray bottle is horrible. Decant it into another spray bottle that can actually mist. You only need to mist a pane, then clean with microfiber. Repeat as needed. Change the cloth when damp. If these are the real leaded lights these ideally are done when either the heating is on full or in summer, as they condensate when cold (in winter), even from the warmth of your hand.
Price them really well, you will really hate it if it's not priced well.