Thanks for the advice. I think it's also reasonable to rule out body, top, etc. and focus on the curtains based on that and the consistent location. But the fact that I can't see it is troubling. Even if this test proves that it's coming from the curtains, I guess my question is WHERE on the curtain. I suppose I can get the film and just line it up to the leak with the proper upside-down orientation and smother it in fabric paint or something like that in that area. But I already have one curtain with some patching on it and I worry about patching it up too much. Maybe I should just get over that fear. The worst thing that can happen is that I'll need to replace the curtains anyway.