Old greasy undercoating?
The OEM undercoat smells and feels like roof tar. I removed some with heat and a plastic scraper
If it gets trans fluid on it, it might become oily?
Just today I removed the old foam tape from under the windshield trim on my 67 dart convert.
The foam had turned to goo.
I used a plastic scraper to get the bulk of it off, then paint thinner. Worked well.
Good luck