Something must really, really not like me.
After looking at that manual and reading it over, I couldn't find anything in relation. I tried looking for a C-clip a little closer, and still couldn't really find anything. Instead of just saying that and leaving everyone who's making their efforts blind, here's a picture of what I'm dealing with. If there's a C-clip there and I'm missing it, something is terribly wrong.
It actually doesn't even look like any of the G36 hop-ups. Those ones I can clearly see where the c-clip is without really having to make the effort to do so. This one seems... well, odd.