Milk Spots, Tarnish, Dirt? Silver Bullion Need Help!

While numismatic quality coins should almost never be cleaned, cleaning bullion is OK. I use a silver cleaner / polish that comes in a small plastic jar and looks a bit like a soap cake. I wipe in on and then off with a soft cloth. It works really well. This compound tends to dry out, become hard, and crack but adding a tsp. of water to it every 6 months or so seems to prevent this and helps keep the material just soft enough to apply easily. Here is a pic of the label on top of the jar: