Sky Light End Bar Cap refitting Question

[swebb99]

Hi I had some sky lights fitting in to my kitchen extension about 5yrs ago and after the recent storms I noticed two of the plastic end cap pieces have come off due to the plastic breaking (see pic)

I've found what looks like replacements here.

I'm concerned that when I unscrew the end pieces that the glass panes will move, is this correct and if so how do I stop this happening as I will be working by myself.

It looks like only the plastic has failed so I assume the sky lights will continue to be water tight even if I don't replace the plastic pieces ?

Thanks

 

[crank39]

The glass won't slip, there's enough clamping force on the top caps for the 30secs the end cap will off

 

[swebb99]

Great thanks I didn't even realise they were clamped, never had a chance to watch them get installed unfortunately