Leaking stained glass window
What kind of window is it? Do you know if it is lead came or foil construction? Is it an outside window? Is it double or triple glazed or just the stained glass? If it is lead came, is the putty flaking out from under the lead? If so, replaceing the putty should take care of the problem. The best way to do this is to take the window out and lay it flat on a work table. Then (assuming the lead is all still good) use a dentist's pick to clean out the loose and flaky putty. Replace with putty made from whiting (calcium carbonate) and linseed oil. Force the putty under the leaves of the lead came with your thumbs and finger tips. Use a sharpened wooden dowel to run around the edges of the came. Roll putty over the window to pick up the loose putty you just cut off with the dowel. Sprinkle a SMALL amout of dry whiting over the window and brush with a natural bristle brush to clean and polish. Turn it over and repeat on the other side. Leave the panel laying flat for a week or so, turning it daily so that both sides dry.
If it is foil construction, it will probably continue to leak. I don't know of a way to fix it.