I like PizzaGuy's idea of the 'park' switch being the issue, reminded me of friend's old porsche with same issue.
He threw a lot of money replacing everything, no change.
Someone told him the switch wasn't grounded and to put a ground from the wiper motor to chasis. It worked perfectly.
OP did say motor was replaced and same problem, grounding may be an issue?
I found this article of interest:
https://www.rockauto.com/genImages/1...erProblems.pdf

Worth a try.