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