In the bottom of an old camera bag tonight, I found an ancient Kodachrome slide. From looking at it through the slide viewer, it appears to be Europe in the 1940s or 50s. The slide is not faded, but it does have a layer of grime on it. Any of you folks have an idea how to safely clean this grime off? I thought about film cleaner, but I also thought I would ask first before I did anything.