Stain Resized

I have that stain too, but in a different spot. Mine is seen sitting in the right rear passenger seat above the beige plastic pillar in the fabric where the the rear passenger window meets the stationary rear window. In my post about the Active Noise Cancellation issue, I refer to to it as an orange cement. Now, that I've seen yours too, I agree its a stain, but perhaps from water getting in or washer fluid from the rear supply line.

I found a few topics that might relate to our issue in this forum.

Thanks for the pictures, they really caught my curiosity.