There's three pieces: the bezel which holds the Pyrex, optic and Luxeon PCB in place; a spacer (with one fin); and the main body (with two fins). The spacer is the active heat sink for the Luxeon.
Yes, you can see an o-ring between the body and spacer. It's really a flat plastic (nylon?) washer, not an o-ring. The threaded spacer does not seat on a ridge or anything in the main body; only the threadlock holds it in place.
Good to hear you got a good one, unlike mine.