Just changed the right rear spring on my GC.
There is NO need to remove the rear shelf to access the three top strut mount nuts. Just pop out the speaker covers, remove the speakers and take out the foam insulation over the strut mount.
This gives you access to the three 13mm nuts.
I used a small 1/4" ratchet wrench with a short extension to undo the nuts. No problem at all to undo the three nuts through the holes for the speaker. The whole process took exactly 1,5 hours, including changing the spring and reinstalling.
To remove the speaker cover, undo the wiring to the speakers and undo the three bolts took probably roughly 10 minutes...
So you guys can save A LOT of time doing it this way instead of removing the rear shelf.
This video shows how it's it done on a F10. The speaker access hole on the GC did not allow for as easy access as it seems to be on the F10, but still no problem with the 1/4 ratchet. There is enough headroom between the underside of the shelf and the nuts that you can actually have the rathcet and extension underneath the shelf as you undo the bolts. For the front nut you can use the small access hole just above the nut, instead of the speaker hole.