Just found this link which is a good walkthrough without removing gasket. I'm not sure it can be done but giving it a try.
https://forum.ih8mud.com/threads/fix-rear-slider-window-louver-leak-in-10-complicated-steps.1241157/
Hi...looking for advice from fellow 80 series LC owners. I just had all of the weather stripping changed on my LC including the quarter panel windows. I ordered new louvers as mine were a bit faded and thought I would put them on myself. Started this yesterday and now it looks like they should...