I had a 1982 (bought new) VW…
I had a 1982 (bought new) VW pickup that did the same thing. Turned out the paint surface was contaminated some how and the top coat did not adhere to the primer. Was a black finish with light gray primer. They eventually paid me to paint it. But a year later while performing a service the Dealer got water in the intake and trashed the diesel engine... That thing got more than 50 miles to the gallon...