I dug out the box of ingredients and prepared to mix a new batch (one cannister lasts a *long* time). I use the small Nalgene screw-top cannisters, becasue they seal up absolutely airtight, and the *only* comes off when you want it to. The Nalgene cannister that held the hardened and smelly stuff had gone very brittle too. I'm not sure if that's because of the concentrated soap or just prolonged exposure to sunlight when fishing.
New (old) cannister ready, I scooped app. 4 teaspoons of Fuller's Earth into a small bowl (PoD). I added (concentrated) dishwashing soap while stirring until I had a very dry paste that just held together. To try and compensate for the concentrated soap I added water to get the consistency right. I like to be a thick paste that hold its shape when you lift the spoon out. Then I added just half a teaspoon of glycerine to prevent the mixture from drying out too fast.
Even though I added water I suspect it'll be more than able to degrease my leaders.
Once mixed, I simply spoon it into a small plastic bag, cut off one corner and squeeze it into the cannister. I find this is by far the easiest way of getting it into the cannister. I've made a smal leather holder that clips to my vest for cannister, but you can tie a piece of string around the neck of the cannister and attach that to your vest/backpack/chestpack/hippack - whatever your prefer to carry your stuff in.
Fuller's Earth can be bought in stores int he UK (at least I was able to get some when we were last there in 2016) and I believe I remember that Paul said he gets his on Amazon (Hey Dude, maybe you should look into affiliate links - maybe we can take over the world with the revenue we would get from sending customers to Amazon :-). You'll find references to this in many classic books on trout fishing and I was first introduced to it by Paul when we first met some 15 years ago or something.
If you have never tried it, you should - it's better than any of the store-bought products and half a pound of Fuller's Earth will last you forever, so get some and try some.
Have a great weekend!