Trunk Leaks and Strange Goo(?)

My buddy, @Purrius, was trying to figure out a rattling/vibration noise in the back of my 2017 Prius. I had damage repaired from a public garage door hitting my car on the passenger rear quarter panel, tail light, and hatch corner. Looking for the noise, he pulled all the trim out of the back along with the cubby for the spare/jack/etc. I've also been having humidity buildup in the car too, so he pulled the spoiler, cleaned under it, and applied gasket maker to the seams/screws. He also irrigated the drains on each side of it. The humidity isn't as bad, but the rattling persisted.

During this he found some sort of oily substance that resembled coagulated cooking oil pooled underneath it all and inside the hatch behind the trim. (I haven't spilled anything like that back there.) It didn't seem to have a smell we could detect. (He did swab some into a glass vial lol.) Purrius handled it with gloves so no skin injury occurred but I did leave my spare tire sitting in it at one point and the contact abraded off some of the surface rubber so it may be caustic?

It also reacts to UV light with a glow! We think maybe a leak somewhere could have leeched out some adhesive and run off into the space? Google said maybe something for noise damping could glow like that... but it was just pooling places, it wasn't 'applied' anywhere as far as we could tell.

Purrius took the attached photos showing where the oil/water pooled into and the UV glow. Also some of the moisture has corroded some wiring.

We'd love some help pinning down cause, and maybe some solutions on how to stop the leaking or identifying what exactly had pooled there in the first place. (Bonus if we can solve the rattle.)