After sac oil has been jarred for a while it separates into a thick creamy tan color liquid & a dark oily liquid.

Is there any advantage or benefit to bottle separately & use one over the other in beaver lure or predator lures.

I just shake it up before pouring and use it like that. Works great. I never tried to drain off the separate the layers.

Same here.

Kind of like skunk essence. It will separate the liquid from the fatty content. Skunk essence fat has a very high weight density and is difficult to keep it suspended while pouring from a larger container. The skunk glands excrete essence that has been pre mixed and the yellow mustard makes the essence linger longer and hold fast.

Beaver oil over time has 2 basic elements that will separate.The light weight oil will surface and the fatty cream will separate to the bottom layer. This is the material that is kept mixed naturally due to the animals glandular activity keeping it blended so it is ready as needed. This oil blend is used to comb into the animals hair to keep it somewhat water resistant / repellent. If not, it would die of hypothermia since the body would not be able to maintain its needed body temperature in the cold water.

I keep oil from males and females separately, this way the female oil doesn't separate much and male oil is liquid to begin with.

Interesting.

I've never noticed this, but I'm gonna check this out.

maybe it's different with your species but in European beaver, females produce paste-like gray oil and males produce yellowish liquid oil. Even the sac wall structure is different. It's an easy way to define the sex of the beaver in the field, by how wobbly the area below the pelvic ring is. Castors are the same in both sexes.