Castor alone is kind of a yellow, pasty stuff (kinda like dry Playdough), but when
you add in the oil gland (sitting right next to the castor in the beaver) you get a
very rich, musty smell that smells a bit like freshly dug earth. Not unpleasant at all,
and in fact the castors and oil glands of beaver are most commonly used in the
higher end cosmetics and perfumes.
When a beaver wants to mark his "turf", he'll excrete a small amount of both the
castor and oil on top of a small mound of mud they'll push up on the edge of the
pond. As it mixes a sheen from the oil will drift right across the entire pond, and
ANY mature beaver in the area will be checking it out...asap, as beaver are
very territorial.
I have a small jar of castors/oil I mixed up for trapping in the early 90's,
and it still smells just as fresh as it did the day it was mixed.
Castor/Oil is commonly used by trappers for catching beaver, as just a little bit
on top of a home-made mud mound will bring 'em running as soon as it gets dark.