I've got a drill chuck that's sticky, and would like to disassemble
it. The chuck has a rubberized adjustment ring, and the usual
3/8"-24 threaded mount. There was no difficulty removing
it from the drill (after I realized the retaining screw was Torx-20
and not hexagonal).

It's a 3/8" Jacobs HandTite model, and the Jacobs web site only
gives takeapart instructions for other (keyed and precision) models.

Apparently, the body (in addition to the 3/8-24 thread) has
a Torx-40 engagement region at the bottom of that thread.
Probably the body is held by a Torx wrench while the main
ring is removed.

The main base ring apparently cannot be pressed off (it doesn't
protrude enough), but it seems to be pressed in place on
a knurled body (not threaded).

Could the main ring unthread from the body? Maybe after heating
to soften a threadlock compound? That'd explain the Torx feature
of the body. Why does it look like the body is knurled, wouldn't
that complicate assembly?