Brake fluid not oil
Brake systems use EPDM rubber, it is incompatable with hydrocarbons and will swell/enlarge 20-50% if even small residues get into the brake fluid. So there's no hydrocarbons in brake fluid, but certainly some hygroscopic elements, you learn this if you eat without adequately washing after handling brake fluid.
My Fleck water softener has nitril orings, lots, which have only a 10 year usable life. Correct design would have used EPDM, they last longer, and since it's a water softener you'd think it was safe. But the Fleck engineer told me that they had to use nitril because service installers used petrollium lubes installing the orings, and thus ruining them if they were EPDM.
But glycerin, is it universal for elastnomers as a help?
I don't know. But I've got a large agitator soaking in a bucket right now.
I wish I knew what elastnomer was used for these agitators and bellows...