Way to open this kind of ratchet with no visible screws and no visible retainer rings

I'd like to know if this kind of ratchet with no visible screws is serviceable in anyway, i.e. if it can be at least opened to clean it. (The ring on the rear serves as selector). It tried prying up the ring with a flat screwdriver (with and without the release button depressed) but it doesn't seem to budge (up). I have to wonder how they even assemble the thing…

Here are some hi-res photos (well, as hi-res as SE would allow) of the actual head:

Contrary to the answer/suggestion below there are no visible retainer rings on either side. There is room for a 0.05 mm feeler to go all way around, and for the 0.1mm feeler in one spot (where the handle curves) under the rear selector. But even there a 0.15mm would not go in all the way that the 0.1mm one does. The gap space might look bigger, but that's only an illusion because the spinning parts are rounded on both sides. There's no retainer ring that I can feel anywhere.

Here's photo of the rear with the eject button depressed (and held that way with pliers grabbing the inner pin tip). As you can see the real ring is also one solid piece of [painted] metal, with nothing obvious to remove there…

(By the way, I managed to clear enough of it with the feelers, so it doesn't make a rock-dust-grinding noise anymore, but the question how to open this still remains unsolved.)