Just from my basic experience, done a few now but not an expert:
Ball end hook is very helpful as is the PLASTIC flat ended stick. I made the ball end by welding on the end of a 90 degree pick and polished it up smooth.
You gotta be careful not to let the pressure someone's applying on the glass, "get ahead of the rope" - as that rope is being worked out (using that circling type motion) the pressure has to be right there; if the rope person is moving too fast it won't seat as the rope will just start coming out of the weatherstrip freely.You can save it sometimes by stopping and working it in with the tools to "catch up". Keep pressure on the whole pane while you're doing that or it'll pop out.
If it's not seated and you can't coax it in with the flat ended tool (or the ball hook) you may need to pull it out and reset the rope. If there's any cured sealant in your gasket, might have to remove and reseal.
