I think it sensible to pull the air spring out rather than try the job with it all fitted.
Not done the collets and seals on our air springs but I have had previous form on similar fittings.
It's important to get the O rings settled properly and free of strain in the recesses. Any twist or not quite straightness and they will leak or, worse, be pushed out of position by the pipe when you slide it in to the collet. Hopefully ours have well made, good quality, collets but some of the inexpensive variety don't retain the O rings all that well leading to trouble if the pipe isn't in line when you push it in. You really need to see exactly what you are doing whilst remaining cool calm and collected during the execution of the task.
If the floating air suspension tables and similar devices I had to deal with in the past are any guide leaky O rings are almost invariably due to poor seating rather than O ring trouble per se. If the end of the pipe isn't carefully trimmed and smoothed off with touch of taper as per book its far too easy to push the O ring out off its ideal seating position. Theoretically when the pressure comes on everything shuffles around to seal as per book so long as the pipe entry is straight and parallel to the collet bore. Any offset push or odd angles and it's all in the lap of the gods. Sometimes Mr Careless gets away with very poor technique and sometimes even Inspector Meticulous has to go all anal (terrifying thought) to make things come right.
Usually common sense and ordinary care is ample but if Lawyer Murphy has decided it's your turn to be target of the day for one of his crack Gremlin Assault Squads ........
Clive