Just taken some of the interior panels off our '83 Caravelle (drivers door panel, one in the engine bay and the tailgate one) The rest are coming out soon as I fit a camping interior and soundproof it(using irishkeets link and tips-nice one mate

And I too was pleasantly surprised to find lots of waxoil-or something similar
Looks to be identical stuff to that in the pics.
I get the feeling it may be factory applied-not really sure why, when I waxoil I tend to remove everything possible to improve access and the brush it on, I have home applied attempts where it has been hand sprayed in that are worse the useless. This looks very professional.
May be it has been done professionally with a proper compressor, but knowing some of the vans history I think this is unlikely.
Maybe it was a dealer option?