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I had a buddy of mine take a look at my Lumina for the same issue, in the trunk opening and below the rear window. Seam sealer cracked and allowing water in. Also I can see it leaking/starting to rust underneath the taillights just below the rear bumper support. Seams of panels. Might want to look there.    My body shop guy will probably sand blast it, reseal it, then paint.

Just open to vent and close   I not sure if that helps. When it closes all the way the glass drops a little below the roof line. Like it does when it’s supposed to retract back. But obviously never does. 

I'm putting together a comprehensive plan to stave off the rot out of the rear strut towers in my '88 GP SE 5-spd. Background Not sure how well known this is, or if this is a whole W-Body issue or something unique to the Gran Prix's, but this is what I've learned in my research. The factory seam sealer used on this generation was petroleum based, standard at the time, but over the years the petro chemicals leach out of the substrate, which creates micro-fractures in the sealer. These micro-fractures, through capillary action, soak up salt water and hold it tight up against body metal, thus accelerating body-rust in the exact locations the OEM seam sealer was meant to protect. Additionally, there's a void-pocket between the inner and outer sides of the strut towers themselves. Over time, condensation collects in those void pockets due to heating-cooling cycles and the resultant moisture has nowhere to go and thus sits in there and rots out the rear strut towers from the top-side down, while the seam sealer defect eats them from the bottom-side up. My Plan (Please Suggest Corrections) Drop the wheels and struts entirely. Power wash the wheel wells Wire wheel/brush the factory seam sealer away entirely Horizontal shelf where strut tower is spot-welded to the frame Vertical seams Circular seam where the strut mounting studs poke through. Spray wheel well side with Corroseal Use a 360 degree spray head to flood strut tower voids with Corroseal Allow 48hrs for Corrosel to fully react Spray Eastwood 2K Epoxy Primer. Apply from the wheel wells up Apply into the strut tower void from the trunk-side, down Wait 24-48hrs for primer to cure Apply 3M 08367 Urethane Seam Sealer to the same places in the strut tower that we'd removed the factory seam sealer from. Inject 3M 08852 Cavity Wax Plus into the strut tower void cavities accessible from the trunk side w/360 degree spray head Install a GM Buick "F-Bar", part 19417890, across the rear strut towers. Bead weld the "cups" to the "bar" for complete rigidity Unload the suspension by raising the rear of the car before installing the strut bar, so that it will be under tension immediately. That's my plan, it's entirely speculative based on a whole lot of research, so please let me know if you tink I'm going down a bad road, or if there's any avenues for improvement. From my personal research, this aside from catastrophic loss, this generation of Grand Prix's were more than likely to be scrapped out from this design flaw than anything else, so staving this off should help preserve my longevity, but please let me know what you think! Sincere Regards, AJM

right, but what positions does the sunroof go in relation? The switch and relay setup are separate

I ordered one to try. Thank you. I’ll keep you posted if I have questions about it.