Factory undercoating not just on body?

[Broman]

I came upon a head-scratcher as I was prepping parts for blasting and painting for my May 1971 240Z.  All the black suspension and drivetrain parts under the car look about the same, with a standard coat of semi-gloss/gloss paint. Except one part: the front diff support.  This part seems to have the same thick undercoating we've seen before (directly on the metal and under the factory color coat overspray).  Why would this one part get coated with this thick coating?  (And no, it's not a dealer spray!)  And the coating is on both top and bottom of  the support!

 

Here is a major run/drip of this stuff...on the TOP surface.  I broke open the glob with a screwdriver and it's all black inside:

Since this run/glob is at the "peak" of the exhaust hump, I hypothesize that they sprayed the top side while right-side up, then turned it over to spray the bottom, and some excess ran down and pooled at this glob.

And here is what made me take closer notice of my part.  Below is a pic I "stole" from an old posting of low-mileage, unmolested May 1970 car showing the same coating on the diff support, with all the characteristic orange peel!  So I know mine is not a one-off fluke.

So here's the question for hive-mind...has anyone else ever seen any other parts beside the underside of the body coated like this?