Well, I just learned a 20 dollar lesson, cheap if you ask me. My Marin hybrid has the GS100 thumb shifters on it. The right side which derails the cog would sometimes grip and sometimes it wouldn't. I couldn't figure it out, so I took it to the shop. All they did was clean it and re-greased it. Guy said that if there isn't enough grease on it, it will cause the actually shifter mechanism not to engage. I thought that was kind of "different." Oh well, live and learn.