Thanks for the reply. Again, you're the only one responding.
Forgot to mention that I DID, in fact, remove the clip on the one I was trying to pull out. The clip has three "fingers" - one of which actually wraps around the rail (but doesn't actually grip it tight). The Helm manual depicted the clip as open-ended on one side and I could actually see this, so I pushed it the other way - but it wouldn't slip off completely (sliding diagonally it jammed on the rail). Had to bend one of the side clips to fully remove it (hope this is OK).
But then I pulled on the injector for quite a while without success. Maybe I need to spray it with throttle cleaner to help it slip out?
Found this picture on the web. Even though it says 3.8, this is what mine looks like (I'm pretty sure). At first I was sticking a small screwdriver on those notched tabs right near the plug hoping that would free it:
The cylindrical sleeve-thing I was referring to must be the section between the notched tabs clip and the O-Ring. The O-Ring is at the very top of the injector, so you're going to see a bit of the tubular body as you pull on it before the O-Ring finally pops out. And it looks like this is the fatter/thicker O-Ring at the top, so that makes me feel better...