Don Nichols did a demo I watched once. He said the only lure he used was sack oil. Castor was worth to much. He also said the same thing Paul says about the response. Don also said if you missed in one set they did not seem to be leary fo the sack oil in another set.
Years back I targeted nutria. I had one basic set when first setting up. It was a pocket set with a fairly deep step down made high on steep banks so it stayed active in rising waters. Every set got tail oil. I used a no2 trap. Caught a bunch of beaver with the nutes and no need for downers as it is pretty hard for a beaver to chew out of a trap that small.
Ted

I use it very lightly in my castor lure recipe

And stand alone attractant on tough final beaver

Usually sac oil from one of their own colony.

Have used sac oil for years and can't tell a difference in effectiveness from store bought lures. Use it year round.

That it is attractive to the kits would be a downside for me. I'm always trying to avoid catching the little guys.

It works great! I use it on those sharp beavers that have an aversion to lures. It can be used all season long too. It doesn't take much either. I like to make a small slick spot on the bank and using a pine needle, or other small twig, I dip it in the oil and only dab it on the slick spot in three or our places. Then I throw the stick/straw into the water so the oil will spread out leaving a trail on the surface. It doesn't initiate a territorial response. I usually set a foothold for a front foot catch. I don't use 330s, because most of the beavers I use this on are already educated. This is one of those tricks my pappy taught me.

I watched a dude from iowa do a demo on beaver and he cut his sac oil with mineral oil I think. Squirted it out of bottle using sneaky sets. Worked well for him!

Will sac oil keep in a fridge to use the next year?

great topic guys.