Sadly I found the Maxima trunk soaking wet and mold growing inside (nice white, green and black flavors, what gelato is that?). That's what happens when your wife uses the car, thank god she brought it back with all 4 wheels...
I am confident it's not from any rear lights (like other cases I've found searching) or antenna. I suspect it's leaking from directly above, enough to rust where the water lingers below (see photos).
Did anyone run into this? How would I seal up those plastic fasteners? (what a stupid idea btw).
No rust above that I can see.

 

I started working on getting the weather stripping of the trunk reglued and figured I'd do it right and clean the old glue first.
Well now I have to paint it, DO NOT USE GOO GONE on PAINT ever!

 

Since you've already dissected the weather seal, after everythi8ng is prep'd, And use 3M Black weatherstrip adhesive without any gaps to ensure it's not the cause.

Now, take the trunk wall liner off the wall by the rear tire and antenna, look to see if there is enough rust/perforation in the metal to let water in, as the tire turns while driving in wet conditions.

Hope this helps!

 

Thanks for the reply!
No rust above the wheel well/behind the liner except for condensation rust on the rear backrest and strut bolt. This car used to have no rust until it took me skying 3/4 years ago and still has minimal rust underneath.

As far as the trunk weatherstriping, I had some 3M Black weatherstrip adhesive, it pretty much attacked the new paint and after I finished the job (or mess I should say) I went to check on the shelf life of that 3M product - 1-2 years - the one I used I boughy a bit more than 5 years ago, no wonder it was already tacky out of the tube, live and learn...