GS's are held together radially with allen bolts, basically, and a lot of the innards are apparent when you get them off the handlebar. The shifter ring is constrained onto the part that encircles the handlebar, which holds in place by a hose-clamp-like mechanism. So when you slide off the grip (which you do by lifting a corner by pinching it up and sticking a little screwdriver in there, then pouring in a couple ml of isopropyl alcohol and then scootching the grip back and forth so the alcohol spreads, which will get the whole grip off in a few moments) then you slide off a washer that butts against the grip, loosen the clamp mechanism and slide off the shifter ring, and the whole works comes apart in your hands. As I recall, there are only two moving parts and one bending-moment part in a GS.

And yeah, I'm sure he's right about them showing up new in pairs. I hadn't thought about that since I tend to buy used.