I was at the supermarket the other day and started reading the box of a Dr. Selby (I live in Uruguay, that's why I find it at a supermarket). I wanted to find out the ingredients, but I found something in the box that might interest y'all: it says that your should keep it without the lid on, so that the top layer dries and thickens. It said that that way it would last you 400 shaves. Also said that the lid was intended for transportation of the soap.
Just thought all you Dr. Selby fans, especially those not living in Uruguay, might find it useful to know.