||shipping to prevent corrosion, then supposed to be removed by dealer (intended to be temporary). I have no idea what the stuff is like fresh - I think it’s just a waxy coating, but over time, it petrified. I believe it’s also used in firearms preservation. Thanks due to Bernie for advising WD40 and heat - worked pretty well to clear mine out after it being in there for 28 years.
No doubt it did a good job - paint was pretty good underneath.
Here’s when I bought the car June ‘18 (pic from the Autotrader ad):
And one taken just now:
...was finally able to scrub the plenum when it was pulled. Still a few areas to hit, but it’s come a long way.