Working with castor shrinkage is always a big issue.
I buy it all the time and you have it either to dry or to wet.
The worse is when guys tie strings to each pod and trap the liquid inside.
Follow my video and it works for both the seller and buyer.
Funny thing, I used to hear that the buyers wanted that liquid in the pods and obviously to have it leak out you lost weight. I started tying a tiny piece of hemp string around each side and when dry you couldn't even see it as it was the same color as dry castor. Wasn't until later I learned that I was wrong on both counts. Haven't done that for 20 years now.
What I do these days is squeeze out the liquid castor before I even start skinning (it's going to want to come out anyway while you handling the castors). I save this and use it as lure. Next I hang the castors in my cold fur shed for a few days as I accumulate more castor. Then it goes into my drying room on a refrigerator rack laying down. Fan and dehumidifier do their work for about a week, I turn them regularly every day or so. Next I put them in zip lock and freeze them. Just before selling them I take them back out and re-dry them for about 24 hours in the drying room. They are dry but still a little squishy in the interior. Not sloshy though.
As you can see from my pics I take care to get all the shrugging muscle off the castor. On males I remove the penal plug which is that white kind of plastic like piece located just at the cloaca entrance.